This fits with the story I heard from a Detroit oldtimer, how true that story is I have no idea. The original 427 Cobra supposedly was the result of a multiple martini lunch Carroll Shelby had with Henry Ford II and as the article says, the prototype wasn't a very good car. The way I heard it was that while Shelby American developed the 427 Cobra for racing, the production version of the car was engineered at Ford in Dearborn with contributions from Kar Kraft.
The Turd was a stock 289 chassis, CSX2196, retrofitted with a 427. Miles came up with the idea for the conversion after getting waxed by the Corvette Grand Sports in Nassau at the end of the 1963 season. Ted Sutton built the car, and Shelby signed off on racing it after briefly driving it around the neighborhood. The 427 Cobra that later went into production incorporated a wider and beefier frame built at AC Cars to accommodate the big-block V-8. BTW, a substantial number of Cobras sold as 427s were actually equipped with modified 428-cubic-inch Police Interceptor engines.