I got new autometer gauges for my 78 nova. Do I need to drop the gas tank in order to hook up the new fuel gauge?

Two show and go questions: I see many people remove their coolant recovery tanks. Is that a good idea, and how do you best plug the radiator? OR is there a good way to restore the original tank, by soaking it in gasoline, bleach, simple green, etc? I have yet to see a replacement that matches...

Just received my new fuel tank from Classic Industries, but it came with a light coat of oil. So if without the oil would the tank corrode? Should I paint the tank? Prompt reply requested, for I was hoping to install it tomorrow, please. GerryLP:cool: