I have several Stovebolt sixes that are 40 to 50 years of age. I have torn them all down. I have not seen any indications that the modern day fuels have caused any significant damage. While the engine is apart I suggest you take the head into a good reputable machine shop and ask for a three angle valve grind and replace the seats with a later metalurgy that is now available. Go to
www.rockerarms.com and see if they stock a fully rebuilt set of rockerarms on a refinished shaft. They do very good work. I traded with them 30 years ago in Torrance. Now they are in Anderson, CA. If you can avoid it don't shave the head. But do "Deck" the block and check all manifold surfaces. Use good high quality gaskets and I strongly recommend a copper head gasket.
Good luck. I have put many miles on these engines and am a fan of them still.
Normbc9
