Is it the straps, or the bolts that won't come loose? If it's just the bolts, you can get them to break with enough torque and buy new ones from your dealer's parts counter. The part number is N802060-S426 for the U shaped nuts that slide into the channel in the frame where the tank straps attach. I don't have a part number for the bolts themselves, but they should also have those in stock at your local Ford/Lincoln/Mercury dealer's parts counter. I just had the same problem when I had my tank out about a month ago. To save yourself the headache, you should pick up a new gasket for your filler neck while you're at it, since the factory one is almost guaranteed to tear when you remove the tank.