The Mustang's engine compartment was not wide enough to accommodate the massive Boss 429 engine, so Ford contracted with Kar Kraft of Dearborn, Michigan, to modify 4-speed Cobra Jet Mustangs to accept it. Kar Kraft was a Ford exclusive experimental facility that functioned as Vehicle Engineering for Ford's Special Vehicles. Kar Kraft had previously developed the first GT40 MKII (winner of the 1966 24 Hours of Le Mans) and designed and built the GT40 MKIV (winner of the 1967 24 Hours of Le Mans).