Which back plate??

[finsruskw]

Looking at a bison 4 jaw independent lathe chuck 7-850-0600 and wondering which back plate I should get to mount on my 9A w/1.5 x 8tpi spindle.

Most I can find say they are for self centering chucks, what would be the difference when it comes to the back plate?

 

[woodchucker]

see : http://www.cdcotools.com/index.php
machine tooling
-> lathe tooling.
I bought one of their 5" back in 2014 nice and thick, really good cast iron back then. No complaints.
I added a set screw so I can run this in reverse with less worry.
He shows a sale right now too. right on his first page.

 

[finsruskw]

see : http://www.cdcotools.com/index.php
machine tooling
-> lathe tooling.
I bought one of their 5" back in 2014 nice and thick, really good cast iron back then. No complaints.
I added a set screw so I can run this in reverse with less worry.
He shows a sale right now too. right on his first page.

I did get this chuck last winter, looks to be NOS
It's a 4304 Bison, 4 jaw indep. 6.25 dia, solid jaws & plain back.
Forget just what I paid, somewhere around $300 IIRC.

Finally got around to maybe doing something with this after needing a 4 jaw for a job.
Had to use the one I already had though, and this got me to thinking about the backplate for the Bison again.
Would this be what I need?
It's already threaded, 1-1/2 x 8tpi but is 8" dia and I need 6.25"
This is from the vendor listed above.
.Anyone here care to help me along with this or even machine it for me??
I have no clue where to start, turn down to the correct OD I assume?
Thanks!