Fortynine5,

The plaid (tartan) valve covers were supposedly only on some 1963 GMC (6 cyl) trucks. Here are some sightings:

http://www.stovebolt.com/gallery/andy.htm

http://www.6066gmctrucks.org/GMCplaid.htm

http://hometown.aol.com/stovebolt8/page6.html

One of the links above says the trucks with the plaid valve covers were called the "Scotchman Special", a Scot would cringe (they would say a "Scotsman Special").

Tim