Hi Gregg, I actually have the chuck currently mounted on an A1-6 backplate that I use on my Whacheon Lathe. As long as the backplate has a spigot or enough material to machine on the backplate, it will work. The chuck will s a plain back.
You're very welcome Joe, and glad to help. What I was thinking is that the Buck Ajust-tru backplate is quite thick, so that it enters the chuck body deep enough for the chuck's 4 Adjust-tru screws to bear against. This design makes for a very tight coupling with much reduced overhang.
Measuring my 8.25" Buck, entering the chuck that deep means the D1-3 adapter must be about 1.875" thick. Seems to me most "standard" backplates are considerably thinner than that, and may not work for you. I wonder if you may be able to bolt a D1-3 adapter to your existing A1-6 backplate after some modifications?
BTW, congratulations: you're going to love that chuck!
Check out Shars. I just bought one from them for my new Buck 8” 3 jaw. Pretty cheap. Seems like cast iron quality was good. It does need finish machined. I needed to take a few thou off the back face to get the taper fit properly. Then once fit to the spindle, machined the chuck mounting surfaces. Not a bad job.