The designer Shelby experimented with a larger Ford FE engine, of 390 cubic inches (6.4 L) in chassis number CSX2196. Unfortunately the car was not able to receive the development it needed, as resources were aimed at taking the crown from Ferrari in the GT class. Ken Miles drove and raced the FE-powered Mark II at Sebring and pronounced the car virtually undriveable, naming it the Turd. It failed to finish with the engine expiring due to damper failure.
CSX2196 was revised for the show down at Nassau which allowed a more relaxed class division of racing. This allowed the GT cobras to run with prototype Ford GT, GM Grand Sport Corvettes and Lola Mk.6. It was for this event in 1964 that the Fliptop cobra was used. An aluminium 390 cubic inches (6.4 L) engine was used. However, the car failed to finish.