For the crew, it was like a dream come true. When they arrived in France for the Le Mans test weekend the cars had been completed, painted, and fully tested... a luxury that race teams seldom enjoy!
Riding the wave of success from the Mk IVs debut victory at Sebring wasn't going to be easy. Shelby American kept up a rigorous schedule of testing and development at Daytona, Kingman and Riverside. During Le Mans practice the yellow Sebring winner was run with small vertical stabilizers on the rear deck designed to aid high speed stability and numerous carburetor configurations were tested. McLaren was fifth-fastest on the weekend, but still 11 seconds off the pace set by Bandini in the Ferrari P4.
Shelby American and Holman Moody were each assigned two Mk IVs and developed them independently and so numerous differences exist in the cars as they appeared at Le Mans: the number of openings in the rear deck, carburetion, doors, windows and dashboard... to name a few.
And of course the Le Mans cars had evolved from the Sebring winner: rear deck hinged at the back, new nose sections with two NACA ducts, amongst other details.