Not sure these '73 doors would fit a '76 without mods. I had a '77B and, as I recall, there were some differences in the latch hardware which prevented me from using these doors. The later rubber bumper cars had an extra strengthening beam in the door and a secondary anti-burst catch/latch, which, if memory serves was basically a U shaped metal piece on the body of the car and a special round headed post on the edge of the door. On second thought, maybe these will fit but will render the secondary anti burst catch/latch inoperative and I decided not to fit them for safety reasons.
Yes, the driver's side is the one with the rust through. I think I see early traces of the crack of doom at the very top edges of the doors though.
Let me know if you still want to look at them.