The horns on a generator equipped '64 1/2 are totally different from the ones on an alternator equipped car. The generator horns are mounted down low on the strut/frame brace. I've posted a picture of one of the horns on a car along with the location of the relay (IN459.) Lots of customers ask about the location of these parts.
Now-back to the transition thing...our early '65 Mustang Convertible was scheduled to be produced August 10, 1964. This was not too long after the transition from generator to alternator equipped cars. This car had an alternator and the radiator support mounted horns. Since it was produced soon after the transition though, you will note in the picture that it has the strut/frame brace with the holes for early style horns. Just a neat little detail to note.