Ok so we dropped the tank, and pulled out the sending unit.
Being the kind of guy that likes to try and fix things, I pryed the sending unit rheostat open.

Everything looked ok in there, so I cleaned the contacts and put it back together.

I noticed it reminded me of a slot car controller inside.

It started to work, intermittantly.

Upon very close examination, I notice the pin where the hot wire attaches to the flat strap that goes to the rheostat on the inside, rotated on the strap.
When I took some pliers and made a positive connection from the pin to the strap the gauge worked.

Took a dremel tool with a small wire wheel and cleaned the area.

With flux and a soldering iron, I soldered the connection so the pin would not rotate on the strap.

Problem solved.

All the while my friend kept saying "just order a reproduction sending unit from year one"

I said, No, I got it figured out!

I was hoping to find the build sheet on top of the tank, but I guess someone already had the tank out and took out the sheet.

Disappointed about that, but glad I fixed the sending unit.

I kept telling my friend " If a man made it, another man can take it apart and fix it".

This was a "fun fix", and it is the kind of thing that makes owning a classic car a great hobby.

Thanks for all the help, and for the motivation to just pull it apart and see what makes it work.