Brake troubles

Describe the idle. Does it run smooth like a stock engine or does it have a lope like a hot rod engine? "I don't believe there is a bigger cam in it" is very vague at best. You say the booster is getting vacuum? How was that verified? You should remove the check valve from the booster, with the vacuum hose attached either while the engine is running, or remove it and start the engine. Put your thumb over the vacuum check valve and see if it pulls vacuum. Don't just remove the hose from the check valve. That's not diagnosing the check valve. If the check valve has failed so the booster does not get vacuum, there's your problem. Lastly, get a vacuum pump and connect it to the check valve while it's ON the booster and see if it holds vacuum. If it leaks down, or doesn't even pump up, you have a bad booster. It sounds to me like the booster is not working for some reason. I would be concentrating on it first. Once you confirm it or eliminate it as the problem, then move on to the master cylinder. Diagnosing one thing at a time will make it much easier than shotgun guessing. Good luck.