The prototype was designed at the Ford Design Center in Dearborn, Michigan.
The Mach I was a Mustang fastback prototype with an extended front clip, functional air intakes, and a competition-type ducktail spoiler. The stock top was chopped and the windshield angled back a rakish 64 degrees. Quick release filler caps were located on roof pillars behind the fixed side glass. Back glass and deck lid were opened by hydraulics from inside the car. The car had an aluminium honeycomb panel chassis.
The Mach 1 was powered by Ford’s 427 V8 engine.