Bill : I have found, over the years, that the MPC Illustrations rarely, and Assembly Manuals even more rarely, give hardware finishes. However, don't forget to check the Text Section of MPC's. In this particular case (pun intended), the 1967 only MPC showed nothing. But, the 1960-68 MPC netted the attached ; both bolts and lock washers "S8".
As always, it must be remembered that MPC's are Service Parts, which may, or may not, be the same as Assembly Line parts.
Hope this helps, if nothing else in your future searches.
Bob