Following on from the prosealing , I sloshed the tank with 3M 776 , Let it vent and cure for two days, etch primed the exterior then installed the sender unit, the pickup tube and the vent tube before finally installing the access panels with cork gaskets and gasget seal.
The big moment, how much fuel did it hold?
I fiiled the tank with standard fuel and let it sit overnight to look for any leaks. I was very relieved to find that not only were there no leaks but that the natural pressure build up due to evaporation and temperature change was very evident by the gas presure release when it came time to drain the tank and I removed the cap.
I measured approx 28 lit. Nearly not worth all the extra work, but as they say the only time you have too much fuel is when you're on fire!