In late 1966, Ford designers prepared a Mustang concept to preview some of the design updates coming for the 1969 model. The Mustang Mach I was a two-seat fastback with an aggressively looking chopped roof profile. Each of the rear pillars featured a flip-open racing-style gas cap while larger than normal air-scoops dominated the flanks. The sloped rear end included a hatchback, a feature that wouldn’t appear on a production model until the 1974 Mustang II.
In the early design sketches, the front bodywork formed a single piece hinged at the front to expose the engine compartment. A 427-cubic inch V8 with four carburetors was meant to power the concept.
Towards the back, the two-position hatchback was intended to accommodate longer objects in a near horizontal position or open wider for cargo loading.
The 1966-1967 Mustang Mach I featured a fastback that sloped down to the end of the decklid and a concave rear fascia similar to the 1967 to 1968 production models.
The production 1969 Mach 1 had a rear window louver as one of its distinguishing visual features. The concept was intended to use a laminated rear window with the louvers embedded within but that idea never even made it onto the concept.
The rear of the Mustang Mach I also traded the twin 3-inch tail-pipes from the initial sketches for four smaller centrally mounted pipes. Additionally, the power-dome hood from the sketches never made it to the show car.
For the 1968 auto show season, the designers crafted a new front end that took inspiration from the 1963 Mustang II concept with its covered headlights and chrome rimmed protruding grille.
The rear end was also revised for 1968 with squared off tail-pipes and a prominent ducktail spoiler.
The production 1969 Mustang Mach 1 had a similar front-end treatment to the 1966 version of the concept as well as the duck-tail spoiler. The side-scoops were significantly smaller and moved higher up on the fender while the roof was similar in height to earlier Mustangs to accommodate a rear seat.