Warning: If you do not grind the push rod guides all the way down you can bend push rods, break push rod guides, break valve keepers and risk complete engine failure if a valve falls. I was saved by the fact that only one of the two keepers was knocked off. We pumped compressed air into the cylinder, held the valve up, compressed the valve spring and reattached new keepers. Grind the valley all the way down to the stem of the guide! Besides being able to properly preload the rocker nuts, it is really tight getting into the back of the engine. It's a bitch pulling the lower manifold but thats the right way to do it.