I don't see anything wrong with the idea, especially if you're thinking a new tank. Guys put them in pickup truck builds a lot, tank sitting on a flat flange of the bed floor, or sometimes beneath the bed floor depending on the look they want. I'd try to cut the floor out to leave the tank flange alone, or massage it to clear as opposed to cutting as much as possible for support. Check YouTube, Mustang Gas Tank in a Hot Rod.