In getting ready to some phosphating I ran across these.
Pic 1 shows two pairs of 64-66 San Jose brackets where one pair has the bottom hook bent outward, the other pair is straight. I don't know any more as these came from an old "stash" of Mustang odds and ends, no hardware was included.
Pic 2 shows a later pair with three out of four attaching bolts, washers and nuts. The bolts, 20546-S, are the ones typically used to attach a bell housing to the engine for 64-68 small blocks, the nuts, 374358-S7, were used only on 64-66 bumpers for the large bumper bolt, and the washers don't seem to have a Ford application, but can be found in the AMK 2014 catalog under p/n B-11754, used for GM bumpers. Based on the nuts being used on 64-66 Mustangs only, these brackets may have been used on 67 models using up old hardware inventory.
Jim