Some gas cap pics fror reference.

If you look at the pics 70 and earlier are nonvented. 71 and later are vented. I put a 73 tank in my 71 and I kept the 71 filler neck and cap on the car. What I did was drilled a hole in the filler tube. put a fitting in it and used a 1970 duster vent tube. On the other car I didn't put the vent tube in and it made no difference. So just use your 71 tube and cap. Steve