You should get and use all of the brake components from your doner car (spindles, caliper adapters, calipers, proportion block, etc...). You should have to do what I did, and swap spindles to the opposite sides from original for caliper/shock clearance. What I mean is the original driver side is now the pass side, and vice versa for the other side. When you are done, the calipers towards the front of the car, not the rear. As far as the booster, you would be surprised what you can find at the local parts store. I was building a 440 for a customer to put into his 84 truck, and the required booster from a company online was about $250. I found the same booster for about half of that locally.
Edit: Just got off the phone with the local parts house, and I can get boosters for the 69 Charger (power disc), and the 76 Volare (power disc 3 versions). If you can't find anything locally, maybe I can help you get one thru me.