From a technical point of view, as it relates to the article, it would be good to see if anyone else sees if the extra "domed slotted washers" being used on 67 and 68 model year cars.
My original previously unrestored 67 SJ car has the domed slotted washers, and I just finished parting out an unrestored NJ car, same thing. Attached is a picture. Same goes for a couple 67 Shelby's I helped on over the last 4 years. The angles involved make something along these lines required.
The body assembly calls out the nut as 359606-S8 and washer as 359972-S2. The 1969 Ford fastener catalog on page 93 calls the washer a "special washer", type 29, with an inside diameter or hole size of 13/64". It is not listed in the 1965 version of the catalog.