When I was in the Army I went on a trip to Alabama and during that time there was a scarcity of 1979 - 1980 fuel tanks. On the way to Jasper to go horse back riding, I had road debris fly up and hit my tank and put a hole in the tank the size of a nickle. Fuel was barreling out of the back of the mustang. I searched and searched the salvage yards and could not find a tank that matched. At the time there wasn't the aftermarket offerings that I see today and I ended up finding a 1982 mustang fuel tank that I made work.
The parts car I bought and cut in half supplied a nice fuel tank protector like the one shown above. Very solid piece of plastic made to take a hit. If you have lowered your car, you are that much more likely to hit something on the highway.
Removing the fuel tank is really easy on a 1979 - 93 mustang. To bands hold the tank and it's just a matter of pinching off the rubber fuel lines and disconnecting them. Then just unplug the wiring occector to the Sending unit. Biggest issue you'll deal with is fuel in the tank. It's best to wait till your almost out of fuel before doing this job.
Late Model Restoration offers a much nicer Stainless Steel Sending unit.