It seems that 1970 is unique; no Hornet gas cap I find fits. 70-72 you'd think would be the same, but it's not -- the cap fits flush with the rear panel, but the recess on the 70 is smaller than 72.
I don't even know what a 1970 gas cap is supposed to look like I've got some generic replacement cap.
73-up has the flip-down license plate -- is that true for all Hornet/Concord through the end of AMC time?