The issue with modern gasoline is that the lead acted as a cushion between the valve and seat. The original head can have hardened seats cut in by a machine shop, then stainless valves. Then you don't have to worry, except for running ethenol. Don't. Ethenol will just cause you headaches. There is additives that are supposed to neutralize the effects of the corn alcohol.
One thing I find it important to add on the subject of valves. Remember that on an F head, the intake valves are in the head, but the exhaust are still housed in the block.