Jon: There have been a lot of publications that show in detail how to check piston-to-valve clearance. I do it in my "Engine Builder's Handbook", but there are many other publications that do the same thing.
The most common way of checking valve clearance is to put a thin slab of clay--1/8 in thick will do--over the valve relief areas. Smear a little
oil on the valve heads, then install a head with an old gasket on that bank and the valve train for that cylinder. Rotate the crankshaft carefully, but stop if there's ANY resistance and investigate.
After you've turned the crank at least on revolution, remove the head and check clay thickness where the valves contacted it with the depth-gauge end of your vernier calipers. This will be valve-to-piston clearance.
There are other methods of doing this check, but the clay method is the simplest and easiest to understand.
Hope that helps.
Good luck, Tom