[deuce_roadster]

If you have tried several original sending units and none work, have you tried changing the gauge? It has been my experience that most of the sending units I have removed from tanks have worked fine, it usually the float that is bad on them. You can bench test the gauge and sender together with small jumper wires. Also, to insure a good ground as the tank sits on rubber, run a ground wire from one of the screws that holds the sender in the tank to something close by to insure a good ground.
All 6volt Ford gas gauge sending units are the same up to when they went to 12 volts. The only difference is the length and shape of the float arm. I will put a chart in my MISC photo album of this which has the adjustments for different cars. This chart came in a box with a NOS Ford sender and expected you to re use the old arm.
note:
I just looked and the picture I uploaded is hard to read, If you need this info PM me your email address and I can send you the file which is easy to read on the screen full size.