a body rear end ? 8 3/4 vs dana 60

Near zero. That's because the weight of the DANA is heavier, but traction issues will not be solved by a heavier rear end. You will need to look into the suspension of the car, the whole suspension.

The cars weight, tire size, etc... All come into play.

Perhaps, if you tell us all about the car, perhaps someone has been there and some that with the same or very similar set up! There's a lot of A body MoPar racers and hot street car set ups here. Someone is bound to know!