On November 19, 1999, about 1330 Eastern Standard Time, a Beech C23, N5203M, was substantially damaged during a forced landing at Fincastle Airport (VA83), Fincastle, Virginia. The certificated flight instructor and student pilot were not injured. Visual meteorological conditions prevailed for the flight that departed Roanoke Region Airport, about 1255. No flight plan was filed for the local instructional flight conducted under 14 CFR Part 91. The instructor stated that he and his student were practicing simulated engine failures near VA83. After the student completed the procedure, the instructor indicated that he was satisfied with the student's performance, and told him to go-around. About 1,000 feet above the ground, the student pushed the throttle forward, and the engine lost all power. The instructor performed a forced landing to Runway 29 at VA83. During the landing, the airplane overran the runway and struck a fence. The instructor added that at the time of the power loss, the fuel pressure gauge indicated "1". He verified that the electric fuel pump was on, but the fuel pressure gauge continued to indicate "1". He also remembered that the fuel selector was on "LEFT" when the engine lost power. He could not remember if he had time to move it to "RIGHT". Examination of the wreckage by a Federal Aviation Administration Inspector revealed that the fuel selector was equipped with two stops, as was required by an airworthiness directive. The stops were installed to prevent the fuel selector from travelling past the "LEFT" or "RIGHT" detents. When the inspector attempted to move the fuel selector into the "LEFT" position, the stop prevented the selector from travelling into the detent. Further examination revealed that three mounting screws for the stop were loose. During a test run of the engine, the Inspector moved the fuel selector less than 1/4 inch from the "LEFT" detent; and the engine stopped running. The Inspector added that during the overrun, the left wing separated from the airplane. The right wing sustained aft spar damage, and the landing gear sheared off. The Inspector observed "plenty of fuel" in both fuel tanks. The airplane's last annual inspection was completed on October 15, 1999.