Unless you've got a pretty well-equipped machine shop, it's best to remove the head and let an automotive machinist check it for you. They will do a thorough cleanup, magnaflux or pressure test the head for cracks, check for warpage, and regrind the valves and/or replace whatever parts are damaged. It's pretty common for engines that sit unused for long periods of time to seize up the valve stems in the guides, or if old, stale gasoline is pumped from the tank the valves can stick after a very short time when the engine is restarted.
One thing that should be done during any attempt to run one that's been stored for a long time is a thorough cleanout of the gas tank, or installing a new tank.
Jerry
