Hi Dan, I am no expert on this, but I have dealt with fuel sending units. I know that resistance changes from full to empty, but I'm not sure what the typical range is.
What exactly makes you think the fuel sending unit is bad? Gauge reading "empty" when you know you have gas?
The first thing is to make SURE the little (4" long) thin wire ground strap is connected to the metal nipple of the fuel sending unit & the steel fuel line. This strap keeps a ground connection in the fuel line where you have a small piece of rubber hose from the factory. It's a good idea to sand both the ground strap & the spots where it connects down to shiny metal to make absolutely sure you have a good ground. You can put a little spray of battery protector over the connecting ends once finished to keep those connection areas rust-free. A smear of Vaseline would work too.
Then, one good/easy test is to disconnect the gas gauge wire from the fuel sending unit & connect a "jumper wire" to it (alligator clip or tiny bolt that fits into the "L" connector), run that jumper wire to a known, good, clean ground (neg of battery for example), turn the key to the "on" position. IF the wiring & the gauge are good, the gauge should go completely to "full", then disconnect your "jumper ground wire" and the gauge should go completely to "empty".
If all that checks out OK, then the problem is in the sending unit. If your gauge is working, but just not reading right, other people on this board know what your resistance should read empty/full/half-tank.