The retractable system was originally designed by Ben Smith, a Ford engineer who had successfully introduced the 1957 through 1959 Skyliner.
Ford commissioned him to build one Mustang retractable. Ford decided not to proceed with the retractable program, because they were having such a big success with the other versions of the Mustang.
Ben Smith later produced a kit to make retractables from coupes. His kit had a Ford Continental look to the rear of the trunk, along with a Landau (square) top at the rear window. When Shelby considered using this system to make the GT350CR (convertible retractable), Jon Wilhelm redesigned the system to have more of a Shelby flair. He made the top less square to look more like a convertible, and he added a Shelby, 67-style spoiler to the trunk lid. This car has the Wilhelm designs. The hardware is mostly billet aluminum, and is heavy duty