At about 1530 Pacific time, a twin engine Beech C55 lost power in both engines shortly after takeoff from Dietz Airpark and was damaged in the forced landing that followed. The pilot was not injured. The pilot reported the airplane experienced a dual engine failure shortly after takeoff from the 2,800-foot turf runway. Following the engine failure, the pilot attempted to land on the remaining runway, however, the airplane touched down in tall grass adjacent to the runway and slid to a stop. The pilot stated he positioned the fuel selectors to the auxiliary fuel tanks during the engine run up prior to takeoff, but did not reposition them back to the main tanks before departing.