What's the best way to bench test my fuel tank sending unit? I would rather use my original than buy a new one.

I used a multi meter set to resistance.
Put the pos on the nub, then the ground anywhere else on the unit.
Then I tilted it to swing the arm.
I believe it should be around 10 ohms full and around 73 empty. I could have that backwards, but that will tell you if it will work.

Of course there are other things that could prevent it from working. The instrument vr, the gauge, wiring to the unit, and ground not being there.

Here's how I did mine:

Sending unit removed from tank

Remove trunk pan body plug to allow the sending unit connector wire to be routed into your trunk

Hook sending unit up to sending unit wire and attach another ground jumper from the body of the sending unit to a good ground (lay your sending unit on a piece of cardboard or something non conductible)

turn on key to power up your gauges

Now with the unit hooked up you can swing the float arm through its full range of motion and check to see that your gauge is reading correctly. You can also make adjustments by carefully bending the little full/empty stop tabs on the sending unit arm.

I believe it goes from 10 ohms to about 75-80 ohms. They give you a little tolerance on the one end according to the factory manual.