I filled my valve relieves with clay on my last engine. Turn the crank over a few times, then measure the thickness of the clay where the valve hits it. You can do this without gasket too just to get a rough estimate. My engine never even touched the clay so I knew I was good. Hope that helps.
Alot of helpful and professional people on this board and not too many jerks. This isn't yellowbullet, so try a little harder to be respectful.