A body guy needs B body brake help.

My 67 factory original 383 formula s has the disc brakes with the 4.5 bolt circle, one rotor is shot, I have surrendered on trying to find a replacement but thought I'd give it one more shot before changing everything to the 73 up style. Anybody know where I can find relatively decent 4.5 set of A body 67 to 70 rotors? NOW for my new dilemma, I just picked up a screaming yellow and black 73 charger 340 clone for a song. My buddy gave up on it because he could not get the brakes to work. He had converted the non power discs to power by adding a new master cylinder and booster combo from kragens, but even after bleeding the brakes and master cylinder the pedal goes all the way to the floor and barely starts to move the wheel cylinders. My buddy told me that this is the third master cylinder booster combo he had tried. I've checked and everything looks fine. With the engine off I get good pedal after bleeding the brakes, but as soon as I start the engine the pedal just sinks like a rock! HHHHELPPP! Raul.