Sounds like the return spring in the master is shot, or the master cylinder pushrod is hanging up.
If the brakes feel good when you push them down and they return fine when you pull up the pedal, then I doubt the vacuum pump is an issue. Is there a "jarring" or an "unhooking" feeling when you pull up, or do you have to pull the brakes up all of the way?
I believe the car has the front disc/rear drum setup if I remember right from seeing it in Foxboro.
I would look into the master cylinder and see if it checks out on a bench test.
