If its the dull grey paint thats normally found on non gen panels this will wipe off with standard thinners.
I am a great advocate of the heritage finish but its always worth having a close inspection of the inner surface to check for spider tracks of rust forming under the coating. (seen this once but it was on an old panel)
As to the finish this depends on what you intend to use as a covering. Etch prime then stone chip followed by top coat and if you want a clear waxoyl.
Etch prime, prime, topcoat then waxoyl if you are after a smooth paint finish. Don't forget etch prime on bare metal only.