The Ford GT40 may have been built to stick it to Ferrari at the 24 Hours of Le Mans, but a handful of road cars were also built for customers. One of the rarest of that breed is about to hit the auction block.

Among the desirable classics at the RM Auctions event taking place during this year's Pebble Beach Concours d'Elegance weekend (August 15-16) will be chassis GT/108, the seventh car built after the first GT40, which featured chassis number GT/101, and one of just four GT40 roadsters ever built. Another GT40 roadster prototype went up for auction in 2011.

In addition to its unmolested condition, this car is significant because it was used by Ford and Shelby American for development work. In fact, Carroll Shelby drove Henry Ford II in this very car during a demonstration for Ford's board of directors at the Shelby American facility in Los Angeles back in the 1960s.

Sold by Ford into private hands via Kar Kraft in 1965, chassis GT/108 has been shown at several prestigious events, including past Pebble Beach and Amelia Island Concours d'Elegance events. It's spent more than two decades in a single owner's collection.

GT/108 retains the modified front end used by road-going 1965 GT40 models, as well as the lowered tail section used on roadsters. It also features the same engine it had when it was first sold into private hands, according to RM.

The company did not release a pre-auction estimate, but given the GT40 roadster's rarity, and the fact that a GT40 prototype recently sold for $7 million at auction, it should be very pricey indeed.

GT/108 won't be the only star at the upcoming RM Auctions event. Other highlights will include a 1931 Bentley 8-Litre Barker Sports Coupe Cabriolet, a 1971 Lamborghini Miura SV, and a barn-find 1961 Aston Martin DB4.