Your LeBlond lathe appears to have very basic 'shell" type bearings. If the rear (LH as you face the headstock) bearing shell is warped, this could be due to some misguided efforts by a previous owner. Maybe prying on the bearing or trying to force it up off the headstock/spindle journal.
The bearing shell appears to be cast from babbitt. Babbitt is a name for a 'family' of alloys of 'low friction bearing metals'. Babbitt is also sometimes called 'white metal'. Babbitt is an alloy which will contain, in varying proportions: tin, lead, antimony, and copper. I am guessing the bearing in the photo may well have been cast from a 'high tin' babbitt.
What I'd suggest doing is to use the bearing cap (the cast iron upper half of the bearing) to press the bearing shell back into shape against the spindle journal.
To do this, I would clean the spindle journal with solvent and wipe clean, also cleaning the bearing cap, and bearing shell. Study the bearing cap to be sure the shell is put into it with correct orientation. It looks like there is an oil hole in the shell that has to line up with the oil hole in the cap. Get things in backwards and possible damage could result.
Try to get the babbitt bearing shell fitted into the bearing cap. You may need to coax it a bit. Babbitt is quite soft, so be careful. I'd use a block of soft pine wood and a light hammer on just the ends (at the split joint) of the shell. Do not strike the curved running surface of the babbitt.
Get the shell into the cap as best you can and put it in place on the spindle journal/headstock. Using the cap bolts, pull the cap down a little at a time, working side-to-side. The idea is to use the cap as a press to bring the bearing shell back into shape. There is some risk of cracking the babbitt shell, so stop along the way and check for signs of damage or cracking. Hopefully, there is enough ductility in the babbitt to allow the shell to be formed back into shape.
If you have succeeded in getting the shell and cap to pull down onto the spindle journal without cracking the babbitt, you are in good shape. If this is the case, tighten the cap bolts with a reasonable pull on your wrench. No need to really pull hard on the wrench as the spindle journals can deform the babbitt if there are no shims in the bearings.
At this point, the spindle will be locked solidly. The next steps are:
-remove front and rear bearing caps with their bearing shells in them.
-using very fine "Scotchbrite' pads, lightly polish the babbitted surfaces in the caps to remove any burrs or glazing. Clean afterwards with solvent and wipe with paper towels or tissue paper.
-clean the spindle journals with a solvent such as automotive brake parts cleaner and wipe with paper towelling or tissue paper.
-apply a very thin coat of 'Prussian Blue' to each spindle journal. Prussian Blue is about like an artist's oil paint, an oil based thin paste. You smear a thin coat on each spindle journal, about like a 'haze'.
-put the bearing caps with their shells back in place on the headstock and snug the cap bolts finger tight.
-roll the spindle about a turn clockwise and then back again.
-take off the bearing caps & you should see a 'contact pattern' of blue spots or lines on the babbitt. This is where you 'read the blue' to determine how good a fit the spindle journals make with the babbitted bearing caps. If you are up for it, you could go the whole hog and lift out the spindle assembly. This will let you check contact on the lower halves of the headstock bearings.
-you should see a pattern of blue spots or splotches and lines, but do not expect to see a solid blue surface. If you are seeing about 80% contact with the blue on the babbitt, you are OK.
-if you see some tiny bright spots in the bluing, these are localized high spots in the babbitt which have made a hard contact with the spindle journal.
-if you have less than about 80% contact or have any of those bright spots, the normal thing is to 'scrape in' the bearing with a hand bearing scraper. This is a curved scraper, and it is used to pare off minute amounts of the babbitt where the hard contact areas with the journal are. Scraping, if done properly, will give a series of 'plateaus' or contact areas and shallow 'valleys' between them. Properly scraped in, the blue on a babbitted bearing will look like a uniform pattern of splotches or spots. If you have never scraped in a bearing, there are likely quite a few youtubes about this online. My own sense is you will find the front headstock bearing to be OK, and the rear cap, having been deformed a bit, may have a very localized contact area and plenty of babbitt not touching the journal at all. This bearing may need a bit of scraping-in.
-When I scrape in a babbitted bearing, I scrape in a cross-hatch pattern for the first couple of tries. Once things 'start to come in' in terms of contact, then I scrape small areas based on where the spots are located. It is common to see what I call a "leopard spot" or two. These are areas where the blue surrounds a completely clear spot. This is an area where a localized high spot made a hard enough contact with the journal to squeeze the blue away, forming the 'halo' around it, looking like a 'leopard's spots'. It's a fooler, but you scrape in the middle (clear area) of the leopard spot and not the area with the blue surrounding it.
-When I have about 80% -90% contact (guesstimating by how much blue vs clear babbitt I am seeing) and the spots have a good distribution over the surface of the babbitt, I 'give the bearing a shave'. I draw the edge of a lathe parting tool blank, or even a 6" machinist scale over the babbitt lightly, in the manner of a 'cabinet scraper'. This 'takes off the whiskers' or small burrs left from the scraping. I finish with a light rub with a fine Scotchbrite pad, then solvent clean the bearing.
-When you have the bearings at this stage, it's time to set the clearances. This is done by shimming. The rule of thumb is to allow roughly 0.001" of clearance per inch of journal diameter. Thus, if you have a 2" diameter journal, start with about 0.002" clearance. Shims can be cut from brass shim stock, or even made from manila file folder paper. You can start off with a bunch of trial shims, enough so the spindle turns freely with your hands with the cap bolts pulled down snug. Note the thicknesses of each shim needed to get the spindle to where you can freely turn it with your hands. Measure shim thicknesses with a micrometer. You can cut shims from soft aluminum beverage cans, olive oil cans, welding rod cans, sheet metal, or heavy paper stock if you do not have regular shim stock on hand. Printer paper as used on computer printers will mike at 0.004", and cigarette rolling paper will be 0.001" thick.
-When you have the trial shims in place and you can turn the spindle freely with your hands, it's time to check bearing clearances. This is done using a dial indicator and something like a hardwood sledge hammer handle, or a pry bar, block and piece of copper. The indicator is set to contact the spindle immediately adjacent to the bearing being checked. You set the indicator so its contact point is at 12:00 on the spindle, with the indicator mounted on something secured to the lathe headstock or bed. Using the sledge handle, you stick it into the spindle bore and force the spindle downwards as hard as you can. The indicator needle may move a bit. Re-zero the indicator after forcing the spindle downwards. Then, pull up on the sledge handle with 80-100 lbs of force (estimate this). Note the indicator reading. This is the bearing clearance. If you cannot get a sledge hammer handle into the small end of the spindle due to the way the lathe is built, or if do not want to try pulling up and reading the indicator at the same time, use a short pry bar to pry the spindle upwards. Put a piece of copper against the spindle to protect it from the pry bar and use a wood block or two as needed to make a fulcrum.
-When you have the clearance noted with your trial shims, you then figure out how much shim to remove to get the clearances where they need to be. Lathe headstock bearings are an interesting proposition as they get 'set up' with tighter clearances than a pillow block bearing of the same material and diameter. The rule of thumb of 0.001" per inch of diameter for clearance usually pertains to babbitted bearings, oil lubricated, on well aligned shafting or similar. Spindle bearings run with a closer clearance. However, since you will have had the headstock apart and had to 're-form' the one bearing shell, my sense is the bearings will need to be 'run in'. Set them up with a looser clearance based on 0.001" per inch of diameter for initial running-in.
-My own test of how the bearings are fitted and set for clearance is to use my hands to turn over the headstock spindle by turning the cone pulley (pin in, back gears disengaged). I lube the spindle with ISO 46 oil (tractor hydraulic oil is what I use and have used for many years). The spindle should turn easily with your hands on the headstock cone pulley. Get the spindle turning with your hands and let it go. It should glide to a stop. If it jerks to a stop, the bearings are likely too tight.
-if the spindle passes the test by turning with my hands, I do a 'bearing heat run'. I set the belt to turn the lathe spindle on the slowest speed, with the 'pin in' and back gears disengaged. I start the spindle turning and use the back of my hand to feel each bearing cap. The back of the hand is used as it is not callused and allows a bit more sensitive feel for temperature, kind of like a mother checking a child's forehead to see if the child is running a fever. If the bearings are getting hot in a hurry, STOP the lathe. Flood the bearing(s) with oil, and loosen the cap bolts. Add a shim of 0.001"-002" to one side of the hot bearing's cap once things have cooled down and try again. The lathe's bearings should warm slowly when running, and at no time should they be so hot that you cannot comfortably put the back of your hands on them. About 10-15 minutes running with no load on the spindle is about what I do for an initial heat run. If the bearings are just lightly warm after 10-15 minutes run at lowest 'direct' (no back gears) spindle speed, I go to the next step on the cone pulley and run another 10-15 minutes. I work up to the fastest 'direct' speed on the cone pulley with no load on the spindle,
-If the lathe bearings pass the heat run OK, I then chuck a piece of bar stock in the lathe and take a cut on it. With a properly ground tool, if I get a good surface finish, it tells me if the bearings are properly set. I face off the end of the stock as well, and if there is no problem facing off with no remaining 'center tit', it is a further proof the bearings are in good adjustment.
-I then take a series of 'hogging' or heavy roughing cuts on a piece of maybe 2"-2 1/2" diameter steel bar. With the bar stuck out of the chuck, no support from the tailstock, it's all on the headstock bearings to properly support the work. Turning a chunk of stock held in just the chuck cantilevers a hefty load off the end of the stock and puts more of a radial (side) load into the headstock bearings. Check bearing temperatures and if the bearings are only mildly warm, you have things setup properly.
-After some running of the bearings with the initial shimming, you should re-check clearances. The journals will have 'bedded in' to the bearings, particularly
if you have done any scraping on the bearings. Simply having had the headstock apart and reshimming, things will want to bed in and clearances will open a bit.
You may find you need to pull out 0.001"-0.002" of shims. After trial shimming to get my clearances set, I usually go back and try to reduce the overall number of thin shims in each 'shim pack'. The more shims you have, the more tendency there is for burrs or wrinkled edges of these shims to give you a false clearance, and a stack of thin shims tends to act like a leaf spring. Once I have my clearances set and know what thickness of shims is needed, I cut the final shims by using heavier shims to eliminate many of the thinner shims. I try to wind up with one or two thicker shims and maybe 3 or 4 thin ones (such as 0.005", 003", 002") on each side of each bearing cap. This leaves me with some thin shims to remove as the journals 'bed in' to the bearings.
-I would not take a diamond stone to the ends of the bearing shell. Try using the cap and cap bolts to press and form the shell back into shape. If, after that, you find some of the babbitt projects slightly beyond the surface of the cap at the split joint, use a file to take down the babbitt. Careful filing is all I'd do.
I'd also take a scraper and put a chamfer on the edges of the babbitt at the split joints. This will reduce the chances of a burr or ding causing the journal to 'stand away' from the babbitt.
-The science of 'plain bearings' (bearings which do not have 'rolling elements') such as babbitt or bronze bearings is quite interesting. In theory, the only time there is 'metal to metal' contact between the spindle journal and the bearing is when the bearing is at a standstill or at very low speeds. As the journal gathers speed, it pulls the oil lubrication between itself and the stationary bearing. This oil form a wedge shape, and supports the journal. The journal is actually riding on a thin wedge of oil. Too tight a clearance and this wedge-shaped film cannot form and the bearing runs hot and can 'burn out' (babbitt can actually melt right out of a bearing). Too loose a clearance and the wedge shaped film collapses or simply can't form and the result is the shaft or spindle wobbles or 'orbits', and the babbitt can be 'pounded out'. If a person is well intentioned but mis-informed or overly enthusiastic about cutting oil grooves in a plain bearing, the result can be a properly fitted bearing that burns out because the excessive oil grooving prevented that wedge shaped film from forming.
The bearing in the photo is quite a piece of work. It was a separate casting. It would be a hard part to reproduce. LeBlond may well have had some steel molds made to cast the babbitt bearing shells in. In the least case, they had a set of foundry patterns and core boxes to make sand molds for casting these bearing shells. For heavy loads at higher speeds with closer running clearances, a 'high tin' or harder grade of babbitt would have been used. LeBlond may well have assembled the headstock with the bearing shells in place, exteriors of the shells fully machined and fitted to the caps, but only 'rough bored'. With the bearing shells assembled in the headstock and shims in place, LeBlond likely then line bored the headstock bearings. This would insure perfect alignment of the front and rear headstock spindle bearings.
Do not try running in dry or 'relying on low speed friction'. It is a sure way to 'wipe' the babbitt in the bearing and stand a good chance of destroying the bearing beyond being able to be re-scraped and refitted.
, put the headstock back on, and moved the lathe to a different location which is where I picked it up. It should be noted that the people I bought the lathe from inherited it from a deceased family member (original owner!) and were not themselves the ones who used it. 
