Early A body Gas Cap

Yes, the later caps are different. The older caps are straight forward, while the later caps have two sets of "tangs" that have to negotiate the notches in the fuel filler neck. The later cap is non-vented.

Stant makes a decent replacement for the later cap for a driver. It has a chrome base and a black plastic cross piece. It paints up well. While the cap delivered with the car was painted the body color, my local dealer only stocked a chrome version. (Like a dummy, I left the original on a gas pump and didn't realize my error til I stopped again for fuel many hundreds of miles away.