Re: Switch beside the seat. My `69 has the same valve, including the electrical wires and capped of fuel line attached to the valve that lead to nothing.
I thought too that at some point the bed had been replaced, but this truck was bought new by my father right after I was born, and I'ld never heard him mention that there was any changes like that.
Might have been part of the Custom Cab package, or the interior package that came with the truck, it's hard to say.
Re: Switch beside the seat. many dealers sold an auxiliary tank that fits outboard of the frame, just behind the cab, the filler neck was accessible in the drivers wheelwell. it didn't hold a lot, and was a pain to fill with the advent of smog fuel nozzles, but they often rusted out, as they were not galvanized. I have seen a few that straddled the frame too.
