You won't bend the valves that easy. Turning it over by hand won't hurt a thing. Don't go forcing anything, but no worries.
Many times, setting the cams on their marks will let you turn the crank freely. Set your cams and then set the crank. If you hit a valve, don't worry. Just adjust the cam(s) one way or the other until you can turn the crank.
Pull the plugs to make turning easier. That way you're not fighting compression and thinking you're pushing against a valve.