Correct. You won't drop the valves to where you can't reach them. You may want to do that instead of using shop air to pressurize the cylinder, but either way will work. You just can't do both unless you seal up all 8 holes or the piston will want to move to the bottom of the stroke from the pressure of your shop air. With the piston at TDC you won't lose the valves though, of that I am sure.
I'll check tonight. I got a bunch of parts in a lot of stuff I bought a year or two ago, and I want to say that there was a pack of Motorcraft valve stem seals in there. I need to check to be sure though.