I'm working on a '68RR. When I got the car it had the original tank in (I believe.) The sending unit never did work. Then my uncle gave me a new unit bought from Herb's Parts. That one was better, but still reading way off. Last year I developed a leak in the tank so I bought a new aftermarket tank. After putting the new(er) sending unit it, it was off. I took it back out and tried bending the float arm. That didn't work, as it still shows E on a 1/2 tank approx.

Later this year things should start coming apart for the body and paint, so I'll play with it one more time. After that, I'll give up. I've even thought about installing an aftermarket gauge near my triple gauges under the dash. We'll see I guess.