'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
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. Ordered vented and non-vented both with no success. Began to give up hope thinking maybe it's just no longer available. It's been a while since I checked, but I don't recall having the extra vent tube. But the car does have under the hood what appears to be the early start of emissions, being born in LA. I have parts arrive 2-3x a week for other vehicle repairs I have going regularly at my place, but this one is getting a bit frustrating. But I'll keep trying...