gas cap

I am also in the same situation: 71 Pre-April gas cap, that will fit an 1 3/8" filler neck and the gap between the gasket and filler neck is 1/4" or less.
I'm not sure about being a Cali emissions car, but I also have the big vent tube in the trunk with the 4 lines in it. I can't find the cap anywhere..
Seems everything on line is for post April 71? Help!! I left mine at a station pump, went back an hour later.. GONE!