Rear End Narrowing ?s

I have an 8 3/4" Sure Grip. I haven't had the pig out in 30 years so my memory of the internals is very vague at best. When switching from tapered bearings to green bearings the thrust block is no longer necessary, right? Would this allow for the axles to be pushed into the housing a bit farther before they are limited by the splines in the diff?

What I'm getting at is, would it be possible to switch to green bearings, eliminate the thrust block, & then be able to have the housing narrowed slightly to get perfect centering of the wheels in the tubs, without altering the splined end of the axles? How much further could they be pushed in before problems would occur? 1/4" per side? 1/2"? Am I totally off in my thinking? I want to keep my SBP & probably would require very little narrowing to make things work.