Just for giggles, when you get the head off, tilt it up so the intake and exhaust ports are facing up. Then pour some solvent, anything will do, mineral spirits, turps, kero, into the ports, you should see leaks out of the valves that are in bad shape.
I myself prefer the copper gaskets but I think that is probably because that is what I have mostly used over the years on these motors. They are becoming a little scarce these days. I have used the newer non copper gaskets on these motors and have not had a failure so it appears you could use either, whatever you can get your hands on.
