Any serious differences that will give me trouble will be how deep the recess is around the filler neck. Chrysler was pretty good about keeping thing standard, but really that's something that can different and not be noticed without measuring it.
I have a friend with a '75 Dart, I'll try to catch up with him this week and measure it and the Valiant side by side to see how much difference there is.
I believe the gas cap changed between 66 and 67 to a deeper cap. The locking tabs on the later models go in to the filler neck deeper. This cap will not tighten on a 66 or earlier A body. As for whats what. Usless has it correct as all 63 to 66 Dodge/ Plymouths A's are the same in the fuel filler area.
