Eight or 10 years ago I bought a new expansion tank from these folks:
https://classicfordradiator.com/61-6...sion-tank.aspx
I wanted to powder coat it but knew the solder melt temp was less than the powder coat cure temp. I 100% disassembled the tank, bought some lead-based solder, some flux and used Bernz-O-Matic propane torch. I melted off and cleaned off all the original solder and rebuilt the expansion tank with the lead solder. And then I powder coated it. No leaks these many years later.
[IMG]
[/IMG]