I don't have a B-body reared in my E-body however, I did mocked up a 15 x 8.5 with 3.75" back spaced using a 275/60/15 tire. The back spacing places the tire too far out-board and it wasn't even close.

From my experience, even sucking in the rear end an inch on each side (depending on which year b-body you are using) and going with a 295/50, you won't clear the fender. According to BFG a 295/50 on a 9.5" rim has a cross-section (CS) of 12.2". A 275/60 on a 8" rim has a CS of 11".

From what I've seen using the B-body rear-end on an e-body you would be better off with something like a 15 x 10" with a 5" backspace wheel if you wish to use a 295/50/15 size tire. If you are going with those Ansens with the 3.75" bs, you may be able to run a 275/60 but I wouldn’t be surprised if they didn't clear the fender lip either.