1971 had two caps, the early (flat) one is in the photo above. The late (after Dec '71) cap hangs over the filler tube about 1 1/4" it's much thicker when you lay them flat. The caps do not interchange, I bought one from the auto parts store for $6 about a year ago.

Sorry, it should read after Dec '70. The filler neck is different because the deep cap would just spin, & not catch hold of the nubs. The car is a November built '71 Satellite equipped with N95.