I went to the U-pull-it yard with a tape measure to search for fuel tanks. I used one from an early 80's Chevy Caprice, and mounted it 90* from stock...with the filler pointing toward the passenger side of the truck bed. GM senders are compatible with most aftermarket gauges, and the tank was for a carbureted model, so no in-tank pump.

I cut a hole through the frame rail and "tubed" the hole with an appropriately-sized piece of pipe (my frame is boxed and stepped) for the filler pipe to pass through. I used a filler door from a Chevy van, with the finger-notch flattened and filled, the door opens with a small solenoid and popper.