Someone brought up using the early (61-67) Econoline vans/truck gas tank instead of a Mustang. The advantage was that it filled from the left side and you wouldn't have to cut a hole in the bed floor for a filler. I liked the idea of putting a later model gas door in the side of the bed instead of having to open the tailgate to fill her. I got the measurements for the van tank. It is 25"x31"x8"deep. There is 33" between the frame rails on the van also. More decisions......