THE PLT STATED THAT SHORTLY AFTER TAKEOFF, AT 500 FT AGL, THE LEFT PROP FEATHERED BY ITSELF, THEN THE LEFT ENGINE QUIT & HE WAS UNABLE TO RESTART IT. HE ELECTED TO DIVERT TO ROLLA, MO & LAND AT THE NATIONAL ARPT WHICH HAD A LONGER RWY. WHILE EN ROUTE, HE RADIOED THAT THE ACFT WOULD NOT MAINTAIN ALT, THEN REPORTED THAT THE RIGHT ENGINE WAS SMOKING. FSS PERSONNEL SAW SMOKE FROM THE ACFT & STARTED THE FIRE/RESCUE PROCEDURE. AFTER THE RIGHT ENGINE LOST POWER, THE ACFT STRUCK TREES, CRASHED & BURNED. AN INVESTIGATION REVEALED THAT THE ACFT HAD BEEN FUELED WITH UNLEADED 87 OCTANE AUTO FUEL. THE OWNER HAD OBTAINED 500 GAL OF UNLEADED AUTO FUEL ON 11/11/82. AN EXAM OF THE LEFT ENGINE REVEALED EROSION OF THE #1, #5 & #6 PISTON CROWNS, BLACK OIL WITH ALUMINUM FRAGMENTS & SILICONE RUBBER GASKET CEMENT, AND OVER HEATING OF THE #4 & #5 MAIN BEARINGS. THE RIGHT ENGINE HAD DETONATION DAMAGE ON THE #3 PISTON, FLAME PATH THRU THE #4 CYLINDER (UNDER THE EXHAUST VALVE), MELTED ALUMINUM ON THE VALVE HEADS & PISTON CROWNS, 2 BRKN RINGS, OTR DISCREPANCIES.