Brian, I added a power setup to my 4 drum Camaro (your 64 should be very similar!), no issue and the brakes work great. You will need to rebuild the drums to make sure they are all properly adjusted and your lines are good. PB will find the issues
Make sure you get a power master even if you can only find disc/drum masters. Putting a manual master behind a booster makes the brakes to touchy. Also, on Camaros there are two holes on the pedal arm, the higher one is used for power (decreases the angle of the shaft, less pressure). I would check your arm, you may need to create a higher hole if the brakes are to touchy after the swap. Luck!
