The pilot reported that the engine failed shortly after takeoff. The pilot made a 180 degree turn and landed downwind on the runway. He elected to land gear up to avoid a drop-off past the runway end. The aircraft slid off the runway end, but came to a stop before reaching the drop-off. Examination of the engine revealed that the #4 rod bearing had failed due to lack of lubrication, although there was oil in the crankcase. The pilot stated that the engine had experienced an inflight loss of oil pressure 2 days before, and he made a precautionary landing. The mechanic who subsequently examined the engine found an improperly secured fitting on the prop governor oil line. He also found 1 quart of oil remaining. The mechanic secured the fitting, checked the oil filter and screen for metal, then serviced the engine with oil. The engine was test run several times then released to the owner. The engine manufacturer states in the engine specifications that the minimum safe oil quantity in the engine is 2 quarts.