Hmmm.....
My own method is to first ask - what did I screw up? I mean, it's possible that some other component decided to fail right now, but usually, it's something I did. Especially as you describe - it was working fine DURING the task, but once you got it back together and rolled it outside, it DIDN'T.
I don't think it'd be a bent valve because that would be hard to turn over as the valve was opened, but then the cam would just turn out from under the valve and resistance would be gone and the valve would hang open.
What else did you mess with? Cam chain tensioner? Points plate on end of cam? When you describe it as "wrench on end of crank" how were you doing that? Thru what cover? And did that cover not go back on right, etc?
Sorry I'm not more help - I don't know much about the 450's, but just generic troubleshooting. Good luck with it.
Kirk