I have my tank out of my '68 right now. I wanted to sandblast and paint it before reinstalling. The tank is empty. Is this safe to do? Do I need to let the fumes escape for a few days??

If you are concerned about fumes, then fill the tank completely with water before blasting. I would take measures to make sure no sand gets inside also (remove sender, plug hole..gas cap on tight, and then the area taped...etc..)When finished, empty the water out, and let it dry up for a day or two before reinstalling the tank.

I would be concerned about sand getting in and also about getting a bunch of pinholes through the tank. Why not get a new tank? At about $100 a pop for a new one, it wouldn't cost much more than sandblasting your old one.