The listing claims that in 1965 Ford had invested around $250,000 in Ben J. Smith's idea to build a prototype model of a Mustang Coupe-Convertible with a retractable hardtop that would be offered as an option in 1967. However in 1966, Henry Ford ll decided to axe the project because the hardtop would not be motorized.
We found an interesting article on the subject on the October 2005 issue of Hemmings Classic Car magazine that confirms the seller's claims. Turns out that Smith and his son Dave had created a handful of retractable hardtop Mustangs before they called it quits in 1996. As for the original 1965 prototype, Smith told Hemmings that it disappeared never to be seen again.
While there's no doubt that a lot of work went into creating the Mustang Coupe-Convertible, we think that the Lambo-style doors of this particular example were an unnecessary addition. If you're interested though, the car has been listed for a second time on eBay.