Near the end of the first flight following installation of an overhauled engine, the engine seized after the pilot noticed a rapid drop in oil pressure. After the accident, the left side lower exterior fuselage was found to be covered with fresh oil, with the oil smear originating near the oil breather line. The engine cowl baffle seals were found installed incorrectly. Less than 1 quart of oil was found in the engine sump. On the external rear sides of the #3 & #4 cylinder barrels, an oval area of heat distress was noted. The crankshaft & piston rods exhibited progressive heat distress on all rod bearings and crankshaft journals, with the #1 rod exhibiting the least heat signatures & the #4 the most severe. The #3 rod cap was found loose in the engine; examination of the cap bolts revealed severe necking signatures at the point of tension failure. A micrometer was used to measure the cylinder barrels for roundness. The #3 cyl was found to be outside the factory spec by .002 inches.