ABOUT 5-10 MIN AFTER TAKEOFF THE PILOT LEANED THE MIXTURE ON A ROUGH RUNNING ENG. ABOUT 30 MIN LATERFTER THE LEFT ENG BEGAN TO OVERSPEED. THE PLT WAS UNABLE TO FEATHER THE PROP. THE PLT RETURNED TOWARD THE DEPARTURE POINT WITH MAX POWER ON THE RIGHT ENG. UNABLE TO REACH THE ARPT, AN EMERG LANDING WAS MADE ON A HIGHWAY, DIRECTIONAL CONTROL WAS LOST, AND THE AIRPLANE COLLIDED WITH TREES. LAST ANNUAL WAS IN 1978. LEFT PROP START LOCK PIN BLADE L3 CORRODED, IN EXT PSN. LEFT PROP PITCH CONTROL CABLE SEPARATED, FRAYED, CORRODED. GENERAL DETERIORATION OF PISTON RINGS AND #6 CONROD. RIGHT PROP GOVERNOR CONTROL CABLES CORRODED, FRAYED. RIGHT ENG #5 INTAKE PIPE CONNECTION AND HOSE MISSING. ALL COMPRESSION RINGS PISTONS #1 AND #5 SEVERELY WORN, TOP TWO COMPRESSION RINGS PISTON #2 SEIZED. NO RECORD THAT THE AIRPLANE HAD BEEN INSPECTED BY AN A&P MECHANIC OR FAA APPROVED AIRFRAME REPAIR STATION. PLT STATED FLIGHT MANUAL NOT AVAILABLE OR USED DURING GROUND OR FLIGHT OPERATIONS.