If you do find that you need a new tank check out these guys. I bought an '86 tank for my '84 efi swap here.

Living in the heart of the rustbelt I have seen corrosion problems with the pump mounting bracket, which is what the pressure and return lines pass through as the enter and exit the tank, on first generation 4runners. Usually the metal lines corrode at that point, but the vehicles are usually very rusy by the time that that happens. The pump bracket holds the in-tank fuel pump and mounts to the tank on top with a circular mounting plate. They retail for about $120 from the dealer. Be very careful if you have to use power tools to remove rusted fasteners from the tank. One spark from the motor brushes of a tool could cause an explosion that would change your life. -- Matt