SPARE TIRE WELL OR NOT

I put one back in my 75 Dart Sport after the po carved it out and put a fuel cell in the trunk. I wanted to return it to the original tank and without the tire well I didn't think the tank would stay in place properly. As for a spare or not, I don't have one at the moment.
I dont recall the tank sits tight against the spare well. Tank might move farther in a accident without the well.