The first prototype, designated in official photos as the 1961 Ferrari 250 GT Le Mans Berlinetta Sperimentale, was constructed from chassis 2643GT, originally a 1961 250 GT SWB. It was built to competition specification, which included a reinforced chassis, a competition gearbox and a "Tipo 168/61" 3.0 L engine tuned to 300 bhp, equipped with dry sump lubrication and six Weber 38 DCN carburetors. Pininfarina constructed a new lightweight aluminum alloy body for this prototype, which resembled that of the 400 Super America coupe. 2643GT was entered by Scuderia Ferrari in the 1961 24 hours of Le Mans, driven by Fernand Tavano and Giancarlo Baghetti. Although they were running as high as 8th overall, they were forced to retire at 4:45 am on Sunday morning due to engine failure. During the course of the race, Ferrari engineers gathered information about the performance of the car which was used to modify and improve it, including the addition of a rear spoiler. During the Le Mans race, 2643GT suffered from high-speed instability, possibly due to the front end design. Following Le Mans, 2643GT returned to the factory, where it was used for more testing. The prototype raced again at the 1962 Daytona Continental 3 hours, where it placed 4th overall and 1st in the GT class driven by Stirling Moss. Subsequently, it was sold to N.A.R.T. and a succession of private owners.