I'm actually doing this same hing right now. I bought a 'dual diahram' booster out of a Cutlass BroHam from AAV. Turns out it was the same part number for a plain regal. The bad part is I found a thread where someone whent from the dual 9" to the larger UFO looking booster and said the brakes were much better. Same thing with the master cylinder, plain Regal. I got a new one made of alum from Oreillys.
You'll need a way to get a vacuum signal from the engine to the booster. I'm going to put a 3/8" brass hose barb on the back of my plenum instead of getting that TTA vac block. The other thing is the brake pedal. You can get a used one out of a N/A Gbody, or modify the stock PM pedal to work with the vac. (that's what I'm working on now).