The Michael Lamm and David Holls classic
book, "A Century of Automotive Style: 100 Years of American Car Design" devotes several pages to the development of the
Ford Mustang. It seems that it was a crash project launched only two years before the April 1964 introduction. A complicating factor was that Henry Ford II was gun-shy regarding speculative products due to the huge losses Ford Motor Company absorbed in its disastrous Edsel brand effort 1958-60. The final styling concept persuaded him to okay Mustang.
The Mustang design was more of a committee effort than usual, but Lamm and Holls praised the unlikely success of that kind of venture known for yielding less-than-stellar results. Mustang was an aesthetic success and, even better for Ford, a sales triumph.
That Mustang would sell 121,538 cars in model year 1964½, followed in 1965 by 559,451 was far beyond the imagination of Ford management. So rather than create an expensive special body platform, it was decided to use the 1964
Ford Falcon compact car as the Mustang's basis.
Unless noted, images below are of cars listed for sale.
Gallery
1964 Mustang Hardtop Coupe - factory photo
The original Mustang design seen on what seems to be a pre-production car. As best I can tell, production 1964 1/2 Mustang grilles included a thin, horizontal chrome bar bracketing the pony.
1964 Ford Falcon Futura 2-door sedan - Daniel Schmitt photo
The Falcon, whose platform the Mustang shared. Both had the same length, 181.6 inches (4613 mm). But the Mustang's wheelbase was shorter, 108 inches (2743 mm) compared to the Falcon's 109.5 inches (2781 mm).
1964 Mustang Hardtop Coupe - Mecum Auctions photo
The Mustang probably shared the Falcon's cowling structure and perhaps the windshield.
1957 Continental Mark II - Barrett-Jackson Auctions photo
Lamm and Holls state that the Mustang's fenderline was inspired by that of the 1956-57 Continental Mark II. The wide Continental C-pillar was often used in later Ford designs, including Mustang.
1964 Ford Falcon Futura 2-door sedan
Front quarter view of the Falcon. Compare to the image below.
1964 Mustang Hardtop Coupe
Windshields appear to be the same, though Mustang's is slightly more raked. That might explain the different relationships of the A-pillar and the door front cut-line -- the base of the Mustang's windshield is slightly forward of the Falcon's. Note the front of the hood projecting forward of the headlights. This helped provide the Mustang with a longer hoodline than would have been the case otherwise.
1964 Mustang Hardtop Coupe
Like the 1961 Continental, raised fenderline sculpting helped to visually "nest" the hood, trunk, and passenger compartment greenhouse. Those three-segment tail lights became a visual trademark for some Mustang generations.