Don't know what the situation is with the year of your car. However, for my 68 and 70, I bought new fuel tanks from Quanta. They look like duplicate factory original tanks. I think they both cost in the low $200 range. Just buying new seems to be the best solution. I painted the outside of the tanks with Eastwoods Tank Tone paint.
I really worry about the 68. Don't drive it that much and the gas in it is 10% ethanol. Friday, I'm going to buy alcohol free racing gas. Hopefully there will be something that's not too expensive. I bet I'm looking at $10 a gallon. We'll see. I've been using Seafoam in it so far. $10 a gallon will be too expensive for a permanent solution. The 68 has a pot metal Holley carb (new). I think that's the critical item.