What was found
PILOT EXPERIENCED LOSS OF POWER DURING CRUISE FLIGHT. EXCESSIVE VIBRATION AND POWER LOSS LED HIM TO MAKE A PRECAUTIONARY/EMERG LANDING IN WHICH AIRCRAFT WAS HEAVILY DAMAGED. FAA/NTSB INSPECTED ENGINE, FOUND NR 3 CYLINDER EXHAUST VALVE BROKEN OFF AT BASE OF VALVE, AND VALVE HEAD BLOCKING EXHAUST IN STACK FROM NR 4 CYLINDER.