DURING A CROSS COUNTRY FLIGHT ON AN IFR FLIGHT PLAN IN VFR CONDITIONS, ENGINE OIL PRESSURE DECREASED AND THE PROP WENT INTO OVERSPEED. THE PILOT SECURED THE ENGINE AND CONDUCTED A FORCED LANDING. HE ATTEMPTED TO GLIDE TO THE NEAREST AIRPORT BUT LANDED IN A WHEAT FIELD APPROXIMATELY 1,320 FEET SHORT OF THE RUNWAY. THE LANDING GEAR COLLAPSED AND THE WINGS AND FUSELAGE WERE DAMAGED. INVESTIGATION PROVIDED EVIDENCE OF OIL SCRAPER RING FAILURE WHICH RESULTED IN OIL EXHAUSTION. EVIDENCE OF OIL VENTING INTO THE EXHAUST WAS PRESENT.