Parts mismatch is a common malady.. My next question is do you know the diameter of the master cylinder? 7/8" , 15/16" , 1" , 1 1/16" , you may need a larger bore diameter to simply move more fluid and also the master must be equipped for disc front and drum rear. If you replaced parts in kind, same sizes with same sizes, you may have just continued the mismatch but from Massachusetts USA, that is simply a guess! But with all the checks/inspections.... it sounds to me like the master is just not supplying enough fluid to make pressure..