In 1963 Dave MacDonald who Shelby had hired to race his Cobra roadster, convinced Shelby they should build a modified sports racing car. They ended up buying Cooper Monaco's and fitted them with their tried and true full race 289.
Like the AC Bristol, which was the basis for the Cobra roadster, the Cooper Monaco was at the end of its shelf life when Shelby came knocking. Designed in 1958 for the 1959 season, the Monaco was the first successful mid-engined sports racer built to accept 2-liter and larger engines.
The Cooper had room for a V8, and several chassis were immediately available. Once the first two rolling chassis arrived at Shelby's shop, the team had less than a month to turn them into contending race cars. The chassis were disassembled and strengthened for a small block Ford engine. The cars carried four Weber carburetors and a BMC/Huffaker 4-speed transaxle, soon replaced by a Colotti 4-speed. The 289 V8 powered Cooper-Monacos were dubbed “King Cobras” by the press.
Shelby only had one day of testing at Riverside before shipping the cars off to Kent (Seattle), Washington, for their debut on September 29.
The cars were fast out of the box, setting track records at Riverside and Kent, but they were not sorted, and both retired from the actual race. At only 1400 pounds the little cars cleaned up. During a three-week span in October 1963, MacDonald outdueled an international field of world class drivers as he drove the Shelby King Cobra to victories in the two richest road races in America, the Los Angeles Times Grand Prix at Riverside and the Pacific Grand Prix at Laguna Seca.
Shelby bought two more chassis, then four more in 1964 for a total of eight "real" Shelby King Cobras. There were four other T61M chassis sold, and they all got V8s, but not through Shelby to make a total of twelve T61 Monacos built.
The cars were not the dominant force Shelby would have liked. The King Cobra was fast alright– that wasn’t the problem. The car handled horribly– there wasn’t enough rubber or weight to handle all that horsepower.