The original fuel tank was made with aluminum, not steel. It probably was a replacement.
The original tanks were manufactured by one vendor, a Florida company. I think the company is Florida Marine Tanks.
http://www.floridamarinetanks.com/ I had a long conversation with the person on the phone while I was ordering my replacement, 15 yrs ago. Come to find out he was the owner. His company makes tanks for large motor yachts. The tank was designed such that if you remove all the tank fittings, It can be lifted out the starboard, or port locker with 1/2 inch clearance if that.
At the time they still had the drawings for the tank, had it in a week, done. The tank with shipping was $190
A buddy of mine had custom foamed in tank on his Tartan 33 S&S design, let go. Had remove all the diesel soaked foam, pull the tank, bring it to a custom shop for fabrication. $800. and 3 weeks
Good luck