In general, 1965 Mustangs used an external tooth lock washer type bolt for fenders and spring shields (officially the upper A arm bumper brackets) attachment. The fender bolts were 5/16-18X7/8 long, the spring shields were 5/16-18X1.0 long. All should be the external tooth type as seen in the one on the fender. The disc type with teeth at the edge were "phased" into production in 1966 where a mix of both type were found in early 66 cars. Smooth disc were not used until 1968. It is possible that the toothed disc type was used in Dearborn in July, I'll let Jeff chime in. All those bolts were phosphate and oil, no cad or zinc finish. I see you have the "nut on the inside option" too.
Incidentally, the nuts and carriage bolts used for the shock tower should be cad or zinc.
Jim