Two thoughts on this. First, I never assume anything on a hi performance engine. And second, I never install a cam or chain without degreeing them in, especially on a hi performance engine. Been burned too many times before I learned those lessons.

And using air pressure to hold valves is a bit risky for a couple of reasons. Have you thought about using plastic rope inserted into the cylinder through the plug hole, then rotate the piston up till it compresses the rope in the chamber and holding the valves. That's the way we do it. Simple and fairly foolproof. Unlike air.