Stop in for a cup of coffee

Rainy Day Auto said
No you shouldn't have to undo the straps.

The filler neck is behind the license plate just like a B body, iirc so the neck should have a little retainer bolt and come straight out.. pretty much has to be muscled out very straight or else it will fight you if it does not come out perfectly straight.

The hardest part is making sure the old grommet doesn't crumble back into the tank.

I didn't remember where the filler neck is on the B's but the early A's unscrew at the quarter panel and the trunk floor panel unscrews as well. I bet most seals can be replaced without pulling the tank. I wonder if Mopar still has them available at the parts counter. The repops aren't quite the right size and can leak.