You really don't ever want to pry engine parts off, since you will usually damage both pieces.
The Valve cover is nuts aren't supposed to be all that tight, when you reinstall them they are to be torqued to 52inlbs. If you don't have an inch pound torque wrench, just hand tighten them using a 1/4" ratchet w/the head of the ratchet centered in your palm.
