If you don't need it to read "Diesel Fuel Only", any fuel gauge from a 73-87 square body PU or up to 89 Suburban will work. My original was stuck at 3/4. Swapped in a spare I had for my 75 C10 and now I have a working gauge. Just have to ignore the Unleaded Fuel labeling. May eventually get around to swapping the back plates.
As others have said, don't assume a bad gauge without checking the wiring and sender. Of course, the gauge is easier to swap then the sender unless you have the bed off.