Fuck that, my old roommate took the gas tank off of his old enduro car with a fucking blow torch... in the middle of the race track.... w/ 1/2 tank of fuel.... no protection.... me and one crew member behind him with extinguishers.
Since we dont have too many, if any, Mustang people on here, id suggest searching for a Helms manual. If you cannot find one, order one or visit a auto parts store and read it there... or a library. You should be able to disconnect it from the filler neck, undo the straps and it SHOULD come right out. I know thats how it is on a taurus. Maybe another bolt or two around the tank meets the car.