Ford introduced its iconic Mustang brand in 1964, but the original concept car didn’t look too much like the finished product.
The concept car, which was dubbed Mustang 1, debuted in 1962. It had quite a few technical and styling cues that were different from the model that rolled off the assembly line in 1964. The car originally had a meager V4 engine under its hood and sleeker front end.
Source
SFGate