[RichardJ]

El Dorado Jim, >> The sending units are available for those tanks, Summit carries them, they are the 90 ohm ones for our old trucks...I installed them in my saddle tanks....and I am only running saddle tanks, I removed the seat tank, and I used a electric solenoid valve from a mid seventies truck to switch the tanks from left to right.<<

Bingo! My plan exactly.

Would love the Summit part number to finish doing the very same.
The tanks have been hanging there for years, but stopped using them when the lines went bad and I removed the valve. Heaven help you if you forgot which tank you were running on when it ran dry. I recently installed an '80s switch, wiring and solenoid valve. Now I need the sending units and replace those ugly old doors. Then, out with the cab tank.

Thanks, Jocko for posting those scans.