Thanks to Chuck, and all who offered suggestions for troubleshooting my "dead" fuel gauge in my '64 Valiant...
I finally got under the car and started checking out the sending unit. I pulled the wire from the sender, and jumpered it to a good ground...
I then went topside and turned on the ignition, and "presto" - the dash unit went straight to "Full".
So, I went back down below, and started scraping a very thick layer of OEM undercoating from the front of the tank, so I could access the sender retaining ring...
When the sended was finally liberated from the tank, it revealed the rest of its story...everything was coated with varnish or "fluffy" brown rust. The float was full of gasoline (and holes /cracks), and the filter "sock" was "peeling" and loaded with "Red mud" (rust).
The sender seems to be electrically functional, so I've ordered a new filter sock and new float.
The next hurdle will be dropping the gas tank and cleaning that out...
Thanks for your help!
De Soto Frank