So as it turns out, it didn’t burn much fuel.
As I’m dropping the tank….  I LITERALLY drop the tank.  It was half full.
Don’t worry though, I caught it with the side of my head. I only broke the piece you see in the pic.
It was the fuel pickup.
Remember, with the relish jar lid.  Yeah, pretty cheesy I know.
We can fix it, we have the technology.

Anyhoo, gauge / sending unit problem was just a matter of totally ignoring the instructions that came with it, and just sort of tweaking it by trial and error.

I knew the tank was 11.5 inches deep.  There was roughly 5.5 inches of fuel.
So I figure that is about half a tank.  So I just kept adjusting the sending unit until it sat between 1/4 and 1/2 on the gauge.  Figured the gauge should show a little less than what is actually in there.