The pilot was completing a visual personal flight. He received vectors to runway 19 final approach course and when the airplane was about 2 miles from the runway threshold, the pilot applied additional throttle. The engine momentarily responded and then continued to miss. The pilot heard a muffled explosion and observed a very small puff of white/blue smoke emanating from the right side of the engine cowling. The engine quit when the airplane was about 1 1/2 miles from the threshold at 2,500 feet mean sea level. The airplane's altitude was insufficient to negotiate the airport and the pilot elected to land in an open vacant lot. The airplane burst into flames after it came to rest. Examination of the engine showed that during the recent top overhaul the mechanics installed the wrong connecting rod bolts that were improperly torqued. The oil drain plug came loose while in flight causing the engine to sustain a catastrophic failure. The mechanics failed to safety the oil drain plug.