PLT PREFLIGHTED ACFT AND NOTED INDICATION OF 9 QTS OF OIL IN CRANKCASE. FLT DEPARTED ROSWELL (ROW) IN NIGHT VMC EN ROUTE TO ABQ. PLT HAD JUST LEVELED OFF AT 6500 FT MSL WHEN HE NOTICED OIL PRESSURE GAUGE FLUCTUATING. OIL PRESSURE THEN BEGAN DROPPING AND PLT REVERSED COURSE BACK TO ROW. OIL PRESSURE THEN DROPPED TO ZERO. PLT SAID ENG STARTED MAKING NOISE AND COCKPIT FILLED WITH SMOKE. WITH SOME PWR STILL AVAILABLE, PLT MADE LANDING ON HIGHWAY WITH THE LANDING GEAR UP. POST-INCIDENT EXAM OF ENG DISCLOSED EVIDENCE OF DETONATION. NR 2 PISTON AND RINGS WERE BURNED, ALLOWING COMBUSTION GASES TO ESCAPE INTO CRANKCASE. HIGH EXHAUST GAS PRESSURE WITHIN CRANKCASE VENTED OIL OBERBOARD, CAUSING OIL STARVATION. THE ENG HAD 2053 HRS OF OPERATION AND 998 HRS SINCE A MAJOR OVERHAUL. ON THE MORNING OF THE INCIDENT THE ENG HAD RECEIVED A 100 HR INSPECTION.