Reading thru all the Ford internal memo's it's interesting to see the evolution of the "project".
I've read often the program was called the "T5", but that appears to have come much later.
The earliest memo dated May 23, 1962 discusses XT-Bird, a sporty car to compete with the Corvair Monza or a "Special Falcon"
key items: max interchangeability with Falcon chassis, introduction 1964 1/2 model in April 1964.
Then in the Sept 10, 1962 memo "Special Falcon Program Outline", they estimated annual volume at 130,000 units/yr.
It leads to the conclusion the main DNA thread is from the decision Ford needed a small, cheap sporty car to compete in the emerging youth market to the "Special Falcon Project" is what became the Mustang. But WOW did they under estimate what that market was, and what huge internal scramble to spin up the production volume, scale up the supply chain and bring on-line 2 additional production plants!
interesting study on program management and the internal decision process to bring a concept to market.
jim p