Some cars deleted the ventilated seats, and at least one (chassis 1049) was built with the opening, metal-framed, windows from the Mk III. The X-1 was a roadster built to contest the Fall 1965 North American Pro Series, a forerunner of Can-Am, entered by the Bruce McLaren team and driven by Chris Amon. The car had an aluminum chassis built at Abbey Panels and was originally powered by a 4.7-liter (289 ci) engine. The real purpose of this car was to test several improvements originating from Kar Kraft, Shelby, and McLaren. Several gearboxes were used: a Hewland LG500 and at least one automatic gearbox. It was later upgraded to Mk.II specifications with a 7.0-liter (427 ci) engine and a standard four ratio Kar Kraft (subsidiary of Ford) gearbox, however, the car kept specific features such as its open roof and lightweight aluminum chassis. The car went on to win the 12 Hours of Sebring in 1966. The X-1 was a one-off and having been built in the United Kingdom and being liable for United States tariffs, was later ordered to be destroyed by United States customs officials. The Mk.II was very similar in appearance to the Mk.I but used the 7.0-liter FE (427 ci) engine from the Ford Galaxie, used in NASCAR at the time and modified for road course use. The car's chassis was similar to the British-built Mk.I chassis, but it and other parts of the car had to be redesigned and modified by Shelby to accommodate the larger and heavier 427 engine. A new Kar Kraft-built four-speed gearbox replaced the ZF five-speed used in the Mk.I. This car is sometimes called the "Ford Mk.II". In 1966, the Mk.II dominated Le Mans, taking European audiences by surprise and beating Ferrari to finish 1-2-3 in the standings. After the success of these Mk.II cars, the Ford GT40 went on to win the race for the next three years. For 1967, the Mk.IIs were upgraded to "B" spec; they had re-designed bodywork and twin Holley carburetors for an additional 15 hp. A batch of improperly heat-treated input shafts in the transaxles sidelined virtually every Ford in the race at Daytona, however, and Ferrari won 1-2-3. The Mk.IIBs were also used for Sebring and Le Mans that year and won the Reims 12 Hours in France.