I had some similar problems with my 56 Ford that I put a power brake setup on. The rod between the master & the booster has to be adjusted to just the right length. In your case, I would adjust it out 1/16" - 1/8" then try it. If that rod is too long, it will build up & drag the brakes. Too short & you'll have to pump 'em. Same thing goes for the rod to the booster from the pedal.