See my post on 4/24. I have pulled the head on the engine and discovered the cause of the frozen exhaust valve was because the valve guide had moved out of position. It had risen up enough (toward the valve cover) to keep the valve from opening, thus the bent push rod. Does anyone have any idea what might have caused the guide to slide? It was very firmly positioned when I drove it out. It was not damaged and the mating surface of the head was good, so I chilled the guide in the freezer and heated the head with a torch then pressed it back into proper position.