James I just had to replace my master cylinder. I used one made by CPP (Classic Performance Products) 4 disc Corvette style cast listed at $59.00, p/n M-C1516-L. They carry boosters as well as lots of brake components. Check them out at
Disc Brake, Steering and Suspension Products for classic Chevy and Ford cars and trucks 800-522-5004. Getting parts is the easy part...changing them out is the pita. I pulled out the side vent which made access to the brake lines much easier and also pulled the steering wheel to get into the pedal box area. Good luck!!
John