83/4 rears lived behind Hemis so the 340 wont hurt it.
An old A-body 8 3/4 has a funky bolt pattern and very hard pressed to find
wheels for them.
A truck 8 3/4 rear with a Sure-Grip say up to 73 has the a good bolt pattern
and you can shorten the housing and cut and re spline the axles.
A 742 case on the differential is what I prefer.
Why not use a NV4500 or NV3500 tranny easyer less trouble.