NOW WE'RE TALKING!
I have posted on here several times that I have seen original paint on these engines/valve covers/ what-have-you that looks very close to the "Pontiac Blue" color by Plasti-Kote. That to me is best characterized as a light blue rather than a gray, but someone in the 50's may have regarded it as being between blue and gray and thence the name.
My vote would be for the lightest (E8FFF) represented on that page, but it is considerably more saturated than that paint chip shown. Of course that chip is a portrayal of colors for HTML text and not really analogous to automotive paint, but it gives an idea.
There is a very good pic someone posted a while back that shows the darker gray too. It is an "exhaust gray" or "dark mud gray" and I have some traces of that on a early '53 splash oiler 235 I have. It IS even darker than the Filling Station paint, with really NO bluish cast, and it in fact has a very flat, matte finish with no glossiness at all.
I have seen just a few Chevy sixes but I have never, EVER seen an "original" one with Gloss Medium Machine Gray or "Ford Gray" like 99.99999% of the guys use!
