Engine speeds up when brake is pushed

I agree with everyone else, the booster is shot. If your gonna continue to run a cam that has 10-11" or less of vacuum when properly tuned you might want to consider doing away with the vacuum assist. If you want to keep it power you can always add a canister that stores vacuum when you decelerate so it's available when you need it. Even if you took that route i would still look into replacing the booster.

P.S. When boosters go, it's internal. You wont be able to seal it up.