1967 #00463 A/C test car, later modified to the '68 Styling for advertisement use. Lots of photos of it (in Acapulco Blue).
I'm not sure if it was also the red car in some ads. I haven't dug into the history recently to help recall it.
EDIT; from the side stripe, I believe that was taken in April or May of 1967, by July it had the typical "GT500" side stripe / lettering.