If you look at the markings left by the washer where it was used, that would be the determining factor as to the type of bolt to use, disc left a ring of small teeth, the external tooth washer left a mark for each tooth, 12. You see the "rings" offset in you picture. It was not uncommon in 1966 to find both as the external tooth type was being phased out to be replaced by the dish washer. There is an earlier type external tooth washer, one with larger teeth but less per bolt, but I believe that was a 65 Metuchen use.
Jim