Materman,
An eBay seller has a 1963 GMC sales brochure for sale and I asked him if it has a photo/description of the Scotsman Special V6 plaid valve cover. He replied that he was a GMC expert and there was no such thing.
I sent him a link to 6066GMC website and he replied = "oh".
GM Heritage Center - as suggested above, try contacting them. My experience is that they know what they have in their library, but they are not broadly knowledgeable "historians" (that would be a lot to expect when dealing with all GM vehicles).
