As far as bolts and fasteners, how strict Ford was when it came to assembling Mustangs at the Factory, I looked at some junk yard 68 Mustangs last week mainly to see the head markings on some bolts, all were built in Metuchen. I studied the bolts that secure the hood latch support and the front 2 grill bolts near the support. I found one car used the bolts with the anchor in the middle for all of the bolts, one car had the "T" design and 4 dots, and used a mix and match of each and my car seemed to use the bolts with the 3 rings and letters "R", "D", "W".
Could it be that Ford used whatever they had laying around, as all of these bolts are the same size.