'71 Duster gas cap question

If you do not have the extra venting tube in the trunk and only have the filler tube you need a vented gas cap. I believe they make them now aftermarket as well.
https://www.autometaldirect.com/1971-Plymouth-Scamp-fuel-system-gas-caps-md-61-c-26_238.html
That's the way my 71 is set up.

I've pulled the trigger on ordering 3x so far from other sources over the last several months. Each time resulted in a return/refund due to unavailability or non-fitment upon receipt.
I went through that too. I got my cap from Jeff @ https://521restorations.com/ The rubber seal rips easily but I scarfed one from another cap that I had bought, didn't fit, and wasn't worth returning.