Thanks for confirming what I suspected on these 1/4's . I did have some 69 Bonneville repro lower 1/4 skins , and they were definitely different . Finding decent / workable
rear 1/4's will continue to be a challenge.
Depending on the extent of rust repair needed an option could be the quarters from a 4 door Catalina, the rear section is the same except for the very top edge on the side running up from the bumper to the roof and the wheel opening is the same (only an inch available at the front of the wheel opening).
if you have the time you can make a wooden template of that nos quarter you have. they you can make a buck to build your own from. i used the chrome trim to get the genra shape for mine.