Oh yeah I remember the Pinto.
Square pistons.
(Okay, “oblong”.. but still.)
Yes, they do need ot rethink how they do things.
But, the NTSC/highway safety mongers probably will want their two cents/pond of flesh in there.
The Delorean had an interesting frame I haven’t seen anywhereelse that could be used in a fashion like you describe, the frame is a box frame, shaped like a double ended tuning fork.
Apply “wet wing” tech to the frame, and you have extra fuel space.
But.. The highway safety commitee will want their say in anything.
On a 2 door coupe there is plenty of air from the vents on the door pillar to accommodate air flow into the quarter panel for the car's computer or other modules elements to operate the car to keep it cool instead of putting it under the hood or engine bay to make room for a spare tire.
Put the car's battery where the hump is in the floor panel on a front wheel car.
Design and reshape, and reinforce the trunk pan to accommodate one or two natural gas tanks horizontally and place a carpet or felt trunk board over it.
It can be done, it's only a matter of will.