This s the biggest no-brainer in Stovebolt history.
Buy a new tank.
Rust blocking the pickup is the least of your problems with an old tank.
Varnish residue on the sides of the tank is the real reason for a new tank. Whatever it is that they are putting in today's 10% ethanol fuel is an excellent solvent for varnish. This will result in migration of dissolved varnish into the check valves of the fuel pump, into the carburetor, and maybe most significantly into valve guides which can cause the valves to seize.
