I have seen some information on the web regarding front frame rail markings (referencing the hook location that the front fenders/guards were hung on) that relates to 65-66 cars. I was wondering if that practice was carried onto later cars and if it was used at all of Fords manufacturing plants?
No not in that fashion.
The ones I have seen relate to SJ cars only.
That is the only Mustang plant that used that practice during 64-66 production. Not sure if other non Mustang plants
Also did the fender/guard have a corresponding number to cross-reference it to the primarily number?...................
Sorry (I'm slow) missed me with that question
Lets see if this will help - The fenders were hung (San Jose) on a revolving track with hooks. It was described as similar to what we see today at the dry cleaners where each hook had a specific number located at the hook. At San Jose the number of that hook was applied (normally) to the front frame rail (a series of numbers a dash followed by a second set of numbers) on both sides of the unibody after the painting of the body had taken place. Each front frame rail received a different number.
In this way the fenders where painted with paint from the same batch of paint that the rest of the car was painted with.
Some later cars/plants appear to have used one of the rotation numbers for the car written on the bottom side of the fender but I don't know (few examples) how long they tried or used that practice at this time