I'm putting a 4 speed in a J body with a 360. I'm using an A body 833 which puts the shifter in "stock" location for a F/M body. A 4 speed hump from a Aspen/Volare fits right in. The hole in the firewall is already there as well.
You could use the B body trans. I'm thinking the B body mount would be too far forward, but the E body one would be better right between the seats. Another option would be to make an adapter plate that mounts the shifter in the A body location using the E body mount, like here:
http://www.bigblockdart.com/techpages/abconv.shtml
For the 8 3/4, a 68-70 B body unit is just the right width and pretty much bolts in. What I did was get rid of the rubber ISO clamp stuff on the springs, and use regular 1/2" center bolts. This way the 8 3/4 dropped right on, using older style shock plates and B body shocks. You could also keep the ISO stuff if you wanted be drilling out the center pin hole in the 8 3/4 perches to the correct size (1 9/16 I think?)
