FWIW

I dug out an article on Gibosn detailing a shaker equipped hemi from the mid 90's.
There is an image in the article with a caption discussing the different nuts used and there being only one type of washer used.

The 70-71 parts book shows a washer being used on the dual snorkel 4bbl air cleaners with a pie tin. Did not see washers in the drawings for the other configurations, some don't even show the wingnuts.

The MMC Guide to e-body fastener book shows a washer with it's dimensions and finish.