Replace this tank?

Shine a flash light on the inside. If there is no rust inside, run it. If there is rust inside replace it because that fine rust powder will cause havoc on your carb.
RockAuto has a tank for $322. Still expensive but better than $400.
https://www.rockauto.com/en/catalog...l+318cid+v8,1241615,fuel+&+air,fuel+tank,6268 That must be an oddball one year only tank. I wonder if you could get away with running an earlier tank and obmit some of the emission BS.