When Ford executive Lee Iacocca asked Carroll Shelby, in Shelby’s words, to “turn a mule into a race horse,” a real race horse this Mustang would become! It was relatively straightforward, but spot-on modifications, upgrades, and component deletions made the 289 “Hi Po”-equipped Mustang 2+2 Fastback into Carroll’s own particular brand of “sports car.” Shelby American built just 562 of those rough and ready ’65s, which were universally considered the “best of the real Shelby Mustangs.” They were not only the first iteration, but they were also the most clear and committed example of Shelby’s original sporting vision for the car.

Most of the production 1965 Shelby GT350s are fundamentally the same. Some of the production cars were delivered with the rare and valuable Shelby-Cragar five-spoke mag wheels, while others had hubcapless steel wheels. Most of the cars wore stripes on the hood and rear deck, while all had manual transmissions and naturally aspired, 306-horsepower, 289-cubic inch V-8s, except for a few.

The story goes that Joseph Granatelli returned to Shelby American’s facility with a supercharged GT350, chassis 5010, and challenged Carroll Shelby himself to a drag race in order to demonstrate the car’s seriously enhanced performance potential. Shelby was to drive a much-lighter 289 Cobra, while Granatelli wheeled the newly muscled Mustang. The supercharged GT350 would dominate the Cobra off the line, not only leaving Shelby in the dust but also duly impressed. He would then place an order for several hundred of the upgrade kits for use on future GT350s (many of which were factory- and dealer-installed on subsequent 1966–1969 GT350s). Estimates vary, but it is often said that the blower package was good for a 45-percent power increase, punching the factory 306-horsepower rating up to just over 440 horses. The die was cast, and the supercharged Shelby GT350 was born.

Shelby chassis 5S425 is one of the two 1965 prototypes to be factory-equipped with a Paxton-supercharged V-8, which could crank out nearly 450 horsepower, making this Shelby GT350 one of the rarest 1965 Shelby Mustangs. According to the Shelby American Automobile Club (SAAC) Registry in which it is featured, the original base Mustang, underlying what would become 5S425, was delivered to Shelby American’s Los Angeles factory on June 4, 1965. Work to manufacture the car into a GT350 began about a week later, and it was completed by the end of that month. Upon fruition, this was a fully equipped GT350 that was finished in iconic Wimbledon White with Guardsman Blue stripes and was wearing the desirable Shelby-Cragar mag wheels.

The car was then consigned to the Paxton products division of the Studebaker Corporation. Then under the control and management of the legendary Granatelli family, Paxton was charged with the development of a high-performance supercharger package option for future runs of the GT350. The prototype equipment was installed on this car, which was one of two such installations to Shelby American’s specification in 1965 (an additional prototype kit was added to a 1966 example).

This Paxton-supercharged prototype was then used as a factory demonstrator before being shipped to Trudell Ford in Warren, Michigan. There, it was purchased by William Kardosh, also of Warren, on July 7, 1966. A year later, in September, it was purchased by Lee Swonder, of Dearborn, Michigan. Swonder decided to replace the original engine with a new 302 long-block powerplant sometime later in the 1970s. The original engine was sold off, although its ownership history has been closely documented by the register. While this Shelby icon was always enjoyed by Mr. Swonder, it was also well cared for during the nearly four decades under his watch. During that time, it was dealt only minor wear and tear, and it is believed that all of the body panels remain original to the car, save for some touch-ups to the lacquer paint.

Thirty-eight years later, the car was still located in Michigan, and it was acquired by the current consignor, and only the third owner, from Mr. Swonder in 2005. The new owner was intent on reuniting the GT350 with its original engine, and after relocating it to California, they accomplished just that. The original engine was reinstalled after having been carefully inspected and authentically rebuilt, but the most critical component of this car’s Paxton supercharger system is the original, unique, and otherwise unobtainable cast-finned aluminum “Cobra” carburetor pressure box that sits atop the engine. Nearly every aspect of the car is as it was built in mid-1965, including its proper paint colors, the correct wheels, and a fully appointed original Shelby GT350 interior. The car runs, drives, and performs as it should, and it remains highly original. Over time, this truly rare car has also appeared in numerous books and magazines about Shelby Mustangs.

The original ’65 GT350 stands out as the purest of the breed, the best performing, and the most sought-after Shelby Mustang, and chassis number 5S425 is particularly unique among them, as it is one of two factory-equipped Paxton-supercharged 1965 GT350 prototypes. If you seek to own the rarest of the rare, you’ll go a long way to find something more unique than this historic, documented, and powerful supercharged muscle machine.