The bolt/clip I've seen on 65 and 66 San Jose built cars looks like the bolt/clip used to hold the rear center of the front fenders to a bracket on the "A" pillar, only longer. That fender bolt/clip in fact it is the same one used to hold the optional battery. The optional bolt/clip is p/n 379924-S2, 5/16-18X1 5/16 in long, the standard is p/n 380582-S2, 5/16-18X2.0 in long. The nut is 55736-S2, the same nut used for the horns. Because of battery acid leakage, the bolt/clip and nut get corroded to nothing in a short time. Replacements were almost anything. I recommend using some Permatex battery anti-corrosion spray in and around that area, and wipe it off for shows.
Jim