Hi Jerry and all on this subject,
The points here are all important,but if you are asking about date or a cut off point,a big clue is the body type....only coupes and convertibles were built with generators and the unique radiator support to vent them.So far we have yet to see any Fastback cars with a generator.As Jeff stated many parts were used well into the 65 calender year so it is not uncommon to see clip on handles and other trim items on later built cars of all body types.In a time frame: March-August 64 would be the window for 64 1/2 if you are able to get a date from the car it will most likely be within this time frame.A visit to the Ford research center a few years ago let me read the radio script for the intro of the new Fastback body type which was released on the air in the first week of September 1964.Hope this answers your question.
Regards R.R