About eight minutes after takeoff, the pilot declared an emergency and reported an engine failure. He diverted, but was unable to reach the airport. A gear-up landing was made about one mile short of the runway. An examination of the aircraft revealed that the vacuum pump was not installed on the engine and there was no cover plate over the opening. Oil was observed along the right side of the fuselage. The pilot stated that a mechanic, who had removed the vacuum pump, had advised that there would be no problems with flying the aircraft without the pump. A teardown examination revealed that the No. 4 connecting rod had failed. The No. 2 and 3 connecting rod bearings were burnt out. The No. 5 and 6 rod bearings were badly scored. The engine oil pump was intact and contained residual oil; the pump gears appeared normal. About 1 1/2 quarts of oil was found in the engine before disassembly.