damn right. the last thing you want is a brand new paint job that pisses a tiny stream of gasoline out the side in a few months.... think of it this way-
you spend all that time shaking soaking and shaking that acid some more to break down that rust and corrosion. all that flaky shit you just dumped out was holding your 30 year old tank together. Most likely the thin walls of your tank are a hell of a lot thinner than they were. YOU HAVE TO SEAL IT!!! urghgh its like 15 minutes of work and a couple days of drying time that will make your life sooo much better.
to answer your main question about the top portion of your tank.... try your best to get that stuff knocked down. but it doesnt really matter now that you took a short cut. just get yourself a handful off petcock filters and some duck tape to seal the sides.