One other thing to consider with the T56 is that most have a 0.5 OD. That means you're probably going to want around a 3.7 rear. The f bodies came with a 5.7, 0.5 6th and 3.42 rear. But with your cam, you would probably be better off with 3.7 to 4.11.
Btw, my old big cam sbc was able to operate lights with only 11" of vacuum.
Btw, my old big cam sbc was able to operate lights with only 11" of vacuum.