[Marco Tahtaras]

Do you have a copy of the Service Bulletins? There is a bunch of good info on the earlier systems. It sounds like you have the equalizer system. In either case it's likely the pedal to cross shaft rod is way out of adjustment. How about the rear rods? Have they been modified as well?

If you have the equalizer (two-piece cross shaft), the brackets that support them below the frame rails allow for minor fore/aft movement. They should be centered in the brackets when the brakes are relaxed. If someone adjusted the rear rods too tight then they will move rearward contributing to your problem to some extent.