77 was a stand alone year on these too. 70-76 had a screw holding them on yes and one screw going into the door. my 77 was unlike that and had 2 screws going into the door at each end of the strap.
Two screws on each side would make it very strong. Funny, though, my daughter's 77 had one screw going into the middle. I think her set up was original. When I pulled the panels they had the original backing paper over the door. Although I think the drivers side had been removed before.
Doug, I don't think what you described is the correct method. There just isn't enough holding that strap to the door. There has to be at least one screw through into the sheet metal of the door. Otherwise, that strap will pull right off.
Also, the endcaps on my daughter's car are chromed plastic. She has the deluxe interior if that makes a difference.
77 and 78 weren't the same. Totally different. That's why I don't care for the 77's. I like the 78 interiors much better. I also don't like that two tone camel interior on the 77's.