I just purchased a 6" 4-jaw chuck on Ebay. It has a plain back, and I have
a backplate that will mount on my lathe that I'm pretty sure I can adapt to
fit the chuck. I *think* I know the right way to do this...but I just want
to make sure.

The chuck has a round recess on the back, and four mounting screws. My
guess is that I can't just use the screws to locate the chuck accurately
dead-center. It looks to me like I should face the backplate so that it has
a round step that will just fit snug inside the recess on the back of the
chuck, which will line up the center of the chuck with the lathe
spindle...., and the screws will lock it in place...

Before I create some scrap...does this sound right?

Todd