Inside fuel tank!

Hi All,
I have 2 rusty RE tanks and plan to repair them one at a time.
One of the tanks is very rusty inside, and has been patched with JB weld. The internal pipe work seems to be so rusty and perforated that it can’t be turned off at the tank.
My mate Mike donated a severely dented FF tank for me to cut open to investigate the internal plumbing, and maybe use the bottom panel and pipe work to weld or solder into the RE tank.