The Toyota internals are built for a particular tank depth...the Ford tank will probably be shallower, if you intend to mount it where the spare goes, and even though you could extend the EFI pump pickup tube, the float arm on the sending unit would not have the same travel as the Ford arm. You might get a rough idea of fuel level, but it would'nt be accurate. It would probably show a quarter tank remaining when you were out of gas.
JC Whitney offers a couple of different sending units that have different ohm-ages (resistance), and the float arms are adjustable for different tank depths. I think the Toyota fuel gauge needs a sending unit with a resistance of 90 ohms.
Liquid gasoline is Not flammable...the fumes, however, are explosive when mixed with air in an enclosed space. When gasoline burns, it's actually the fumes burning on the surface of the liquid. You can weld or drill on any fuel tank safely if you wash it out several times with soap and water, and do your work right away so residual fumes don't have time to concentrate. If it makes you feel better, after you wash it out, fill it most of the way with water...this will minimize the air space inside the tank, reducing the area that fumes can form in. I have welded and cut on many tanks without any problem after taking these simple precautions.
I build high-capacity fuel tanks out of aluminum...my '84 Toyota has (2) 30-gallon tanks under it. I could build you a custom tank if you wanted...but why do you want to relocate the fuel tank, anyway?
