The tie down brackets were supposed to be removed by the dealer, who was to be paid the enormous sum of $1.50 (1960's dollars) to return them to the assembly plant for reuse. As you can see, many were not. There is a bit of controversy about the condition of concourse grade Mustangs (and other concourse grade Fords) that have retained the tie town brackets. Some expect them, and the attaching hardware, to be in a completely restored condition, while others consider them a recycled item and should show signs of wear. To keep from getting minus "dings" on your undercarriage, assume that you were the first user.
For 64-66 Mustangs from San Jose, they were three bolt types and painted semi-gloss black, the bolts natural (all 7/16-14 thread, a light phosphate works), the nuts were zinc plated (the same flange type used on the bumpers for the bumper bolts) and an odd size washer at the frame rail.
For 67-68 Mustangs from San Jose, they were two bolt types and natural (light phosphate works here too, although some may have been semi-gloss black), the bolts natural (light phosphate works here as well), the nuts were zinc plated and a mix of leftover or bumper nuts plus that odd size washer at the frame rail.
Jim
