Maybe GM was ahead of Ford, or had that idea patented. I had a 69 Ford F250 Camper Special, and every time I put the camper on I had to unbolt the hinge to get the tailgate off. Was a real pain. With the 77 F100 I'm working on I modified the gate to slide of 1 side like the newer ones because I tightened up the gaps and the way I had there wasn't going to be enough room to get a wrench in there to remove the bolts.
69 widetrack your right. All he needs to do is open the gate and look at the hinge.