Spare tire well delete

On my 72 Dart been thinking about removing the spare tire well and welding in a flat trunk floor. Reasons are it has a pretty big trunk to begin with. My spare is to wide for the well and sticks up in the middle of the floor. Tire would fit just fine up behind the rear seat like in most B's and all E's. It has inboard springs and not much room for exhaust out the back. Can be done but is a bit tricky. Finally I want a bigger fuel tank. I'm thinking with a flat trunk pan then a Challenger 20 gal tank could work. Would probably have to make a custom fill tube.
Any thoughts? Anyone done this?