The partnership between Ford and Shelby is regarded as one of the most important and prominent in the automotive world. This partnership was built around collaborations such as the Shelby Cobra, the Shelby Daytona, and various successful racing programs. The Shelby Mustang was the mass market's first access to this legendary partnership. Built using a stock Ford Mustang, and making various component and powertrain improvements, these performance oriented Mustangs were offered with 289 or 427 (later 428) V8 engines. The most well known variants were the GT350, GT500, and GT500KR, but the GT350R, and GT350H also made their mark. These cars were built in three evolutions: 1965-1966, 1967-1968, and 1969-1970. Many originals are available on the classic car market, with values reflecting different factory specifications. It is common to find Replicas of the Shelby Mustangs, each with its own degree of authenticity and customization. Due to these variations, these car's values vary greatly depending on their individual provenance and require a case by case scrutineering. As the Shelby Mustang has gone on to become on the most iconic Twentieth Century cars, a raft of Continuation cars have been made which feature the classic Mustang styling, but with modern safety and performance.