I had about 4 valves stuck on my 57 235 and got them moving with a lot of tapping with a ball peen hammer and Kroil spray penetrant. One was stuck down and I rolled the engine by hand and pushed it back up w/piston. It popped up and I just kept working it. Got a few bent push rods that I will replace this week. I have always followed the don't fix it if it ain't broke thinking. Why change out a good push rod? I know the valves were stuck and that is what bent mine when I pulled it to try to roll the motor over.