Valve-Piston distance

I saw a kid on another message board that I know destroy a really nice brand new engine by not checking this and/or not using a degree wheel. I felt so bad for him because he's one of those kids that never has any money...there he was all proud of his new motor with all of the good parts he saved up for....gone.

So good point! BJ, if you need help with any of this, please post pictures and questions man, by all means.

Thanks for all good answers.
The Engine had a prette new camshaft and timing gears/chain when I bought it, so I will just replace the camshaft without changing the timing. will just remove the gears and chain carefully, and put it back on again.
But I will definately try to mount it together and turn it by hand to see if the valves touches the pistons.
I will also have to check the pushrod length. I am changing the rockerarms to sealed power SLP-R-861 and SLP-R-862. they look like some of the ones I had. (It was two different types before)
And I will definately ask before I do something stupid, thanks