I have a 1978, and had the same problem. It became evident what was causing it when I looked at the door alignment to the frame, which proved proper and visibly inspected the door hinges/replaced the sacrificial bushings and installed new pins. Next I put the car on a lift at pep boys and the gap between the front fender and door changed. The front frame mounts were the culprit. So, before you go changing things, conduct that step process of ensuring the door is correct first, then jack up the front and unload the front frame to reveal a possible root cause as opposed to chasing afender alignment that may be correct!
