On November 10, 1994, at 0930 central standard time, a home built 2/3rds scale P-51D, N51K, was substantially damaged during a forced landing near Seymour, Texas. The commercial pilot was not injured. Visual meteorological conditions prevailed for the personal cross country flight. There was no flight plan filed. In the pilot/operator report, the pilot stated that he was in cruise flight at 4,500 feet MSL with "everything indicating normal." Approximately 49 minutes after takeoff "a pop was heard and the engine began to overspeed. The power was reduced to 4,500 RPM"; however, "altitude could not be maintained." The pilot subsequently executed a forced landing to a field, during which both main landing gear collapsed. An examination, by a Federal Aviation Administration inspector, of the aircraft revealed that the propeller speed reduction unit had failed. The aircraft experienced damage to the frame, landing gear, and wings.