You are at an advantageous point in your troubleshooting. Pull the pto off and check it by loading it running up a hill. If that makes no difference, triple check the timing. Overheating is all due to good electrical parts and timing in my experience. Well, as long as engine and fins and shroud are clean.. Seeming as little is left, check your valve clearances. Maybe the lifters got switched intake to exhaust.
