After that long the gas tank is probably rusted. You may want to either stock up on cheap fuel filters, and learn how to replace them quickly along the side of the freeway - or get it cleaned out and sealed up.
Don't put gas tank sealer in before removing rust from the inside... My '48 Willys had that done, and now it's plugging up the filter with strips of the sealant material. I had to replace the tank.
60's? 80's!
-Boyo
