vented -vs- unvented gas cap 72 Scamp w/ 318

My buddy owns a 72 Scamp with a 318. The car has a chrome gas cap that is a little scratched up and he was wanting to replace it. While at the Mopar Nationals 2 seperate vendors told him the chrome caps they were selling would not work on his 72 ? Can someone tell me what the difference is and what would be the proper cap for this car? What would occur if he wwas to have put the wrong one on ? Thanks in advance for any responses.

H Ron!!

I'm not real sharp on A bodys, but I'm pretty dang sure it should be a non vented cap AKA "pressure-Vacuum"

The fill is on the quarter panel right?
There are some different configurations also on the cap it's self too I'm betting.

Sorry can not help much more than that.

My 72 Dart (california emissions, fwiw) vented the gas tank thru a charcoal canister int he engine compartment. So either style cap would work fine for my 72.

Here's a 71 FSM for dart and challengers and other's. Not sure about scamps, but I'm betting they are the same.

And here the same section for 74 dart, challenger, etc.

There was a change in A body gas caps between '71 earlier and '72 later, IIRC. Maybe multiple changes in the few years after '72. If they are selling the early style, they may be correct.

Thanks for the help guys !