I remember not being sure about this back then, all those years ago, and I am even less sure now.
I do remember never taking anything apart on the fuel tank. So yes, the sender should be the original gas one (and the tank is also the one that was originally on that gas car).
I'm pretty sure there was something wrong with the gas gauge out of the original gas cluster from that car, thus I used the diesel gauge. I think the diesel gauge worked more reliably -- but worked backwards. Is that right?
If so, I think your idea of trying a known good gasoline gauge makes sense as the place to start.
