Again, I'm not sure of the actual code... but I'm sure they use the same paint as the V8's did. The best source for this correct paint is Bill Hircsh http://www.hirschauto.com/ they produce engine paints for up to 200 degrees higher than any other product I've found...
They list them by year, and there is some slight discrepancy there... but for the 67/68's it's the light metalic blue, and it's quite clear on thier web sight.