I re-painted the top of the gas tank, making sure to mix enough paint this time. In a day or two when it is dry, I will sand and buff it again, and the tank will be ready for installation.
I also rebuilt the gas gauge, which is a clean, simple, and pleasant task. It’s the world’s simplest gas gauge: there is a float on a lever, which moves a little panel labeled with “0 1/4 1/2 3/4 F”. You look through a little glass porthole to see the numbers inside the tank.
The paint in the engraved numbers had long ago fallen out, so I cleaned up the parts, put a layer of epoxy paint over the little panel, and once it was dry, I sanded off all the paint that was outside the engraved numbers. Now it looks as good as new.