Thanks for all the info. I received my tractor and engine service manuals today so that will help a lot.
When my valves are open and I try to move them side to side they have quite a bit of play. they may need replaced. I pryed up on the bottom of the bushing with a screwdriver and removed the clip with plyers but the valve, spring and bushing assembly doesn't want to come out. Is this a common problem? If the bushing is stuck and needs to be driven out is it possible to remove the cam and then pull the lifters out of the middle, compress the spring and remvoe the keepers, remove valve and spring and then be able to drive it out?