Something's not quite right, as fastbacks weren't around until the production began of the true 1965's, sometime in late July/early August 1964. This picture can't be from the Mustang Reveal when the World's Fair opened in April, 1964.
There were fastbacks early in production. I have pictures of one somewhere but on film. It was at our Asheville Civic center had production date before July and had generator and all the other 64 1/2 differences. He was somewhat of a collector had one of the Factory racing 57 T-birds that ran on beach in Daytona. If I recall right he lived in Fla. it was a cream color.
When I talk with Gale Halderman again I will ask specifically about that. He told me last year that when they presented the fastback to Iaccoa he said "we've got to do it." I think Gale's first sketch was the fastback. I have his book I will look in it. I have seen pictures of prototypes with T-5 signs in front of fastbacks on the internet also. Some of the just bodies used in the worlds fair display were sent back to the factory and finished and sold. They are the ones that bring big money. Made from the prototype tooling. There are actually 3 different hoods used the first year. The very early car hoods sell for thousands. The second edition was the one with the radius not hemmed in the front next to headlight and the 65 was hemmed.
I believe I have a program from the Ford display from the Worlds Fair I will have to see if I can find it and see what is in there.
Ok went ahead and pulled Gale's book out. On page 54 the same picture is there with the red fastback. Under the picture it states, "Visitors were greeted by this fastback Mustang near the entrance of the World's Fair in New York City. This was where the Mustang , in all three offerings (convertibles, sedan, and fastback) would debut to the world. Photo Courtesy John M. Clor / Ford Performance Communications Archive).
There is another view on page 55 showing the lines going into the display with the fastback in the background.
Gale states in his book it was officially released about 4 months after the convertible and sedan.
Some glare on the pics of the book. I ordered an early copy from the MOM, Mustang Owner's Museum, cost is $42.95 but is written my by the people who did the work not MM, lol.
Also note in one of the clay models had the Cougar emblem in grill. Was changed at last minute to Mustang.