It appears that the stud has a phosphate and oil finish that was started in 1968. The studs have the same dimensions for V8 cars (289, 302, 390) for 1965 thru 1970, the earlier cars being clear zinc (ref 370971-S8 and 382717-S2).
Note: Ford's procurement documents specified sizes, materials, finish and a single source vendor so if a change in any of those was made and new part number was created. It was easier than going thru the change procedure.
Jim