The second link is to an engine painted something like GMC 6 cylinder reddish color.
A shade of gray is correct for a 1953 truck engine. The exact shade is under dispute by different experts who studied different original 216/235 truck engines.
I think a low pressure truck engine is a shade of gray like the one in your first post (some think it had a little blue in it). I think a high pressure truck engine has a lighter shade of gray,
much like this older Ford engine gray.
Paint it whatever shade of gray suits your tastes/beliefs - no one has a formula nor knows for sure what shades of gray were used.
