For the 1967 model year, Ford first offered a big-block engine into the Mustang ... The Cobra Jet cylinder heads were unique but based around the design of the 1968 Cougar 427 heads.

Purists of the brand will say that real Shelby Mustangs were not made until the end of 1968 after the Cobra Jet made its way into the Mustang and ... and a 427 Sidewinder aluminum intake.