This is why we offer over 400 different specific applications. Many of the early muscle cars did not have power brakes. Power brakes were an option on 1967 and later models. Because of the increased valve overlap used in higher horsepower engines developed in many cars, there was not enough vacuum to run the boosters. Many of the restored muscle cars have the same problem.
Manual disc brakes work fine.
Boosters are designed to use less effort to stop. We offer many kits with manual or power disc brakes. When installing or replacing a master cylinder, it is critical that all air is removed from the master cylinder. This can easily be done by bench bleeding the master cylinder prior to installation. Make sure it is level.