well, I took your advice and listed the gas tank on ebay:
But ebay is an idiot... I fed in the dimensions and weight and it said it would ship in Canada and the USA for between $100 and $150, so I listed it and now it says it's going to cost $350 to ship it to the same city I live in... hopefully a realistic number appears if you look at it from a US location...
Also, if anyone here ends up buying it, when you're swapping the guts, you have to remove the fuel pump first, the larger port, because when you take the fuel gauge out the base plate kind of has to go back inside the tank through that hole when you're wiggling the gauge out. And vice versa, put the gauge in first, then the pump.