My 428 PI in my Cobra was the dark blue. I looked at some color charts and the 1606 looks correct. Everything was painted except the valve covers. The valve covers were chrome with 427 emblems.
Here is a response that I found on a Mustang website.
For many years prior to 1966, Ford engines were color-keyed to specificapplications and carlines. For 1966, this practice changed, when allFord engines were painted Ford Corporate Blue. Instead of color-keyedvalve covers and air cleaners, the entire engine would be Ford Blue,like the Ford Blue Oval and the Ford Blue offset dealer signs popping upin 1966. Ford's message for 1966 and beyond was simple--if it is blue, itis power by Ford.
As in 1964-'65, Ford continued to paint the valve covers separate fromthe engines. Engine long-blocks, which included block, intake manifold,heads, and
oil pan, were all painted Ford Blue, a darker blue thatcovered all hardware except the valve-cover bolts. Valve covers wereinstalled toward the end of engine assembly using natural metal boltswith integral lock washers. We've learned through observation andconversation with restorers that Duplicolor's Dark Ford Blue (1606) isan accepted color for '66 and later Ford engine restorations. Analternative, when Duplicolor isn't available, is Krylon's Dark FordBlue, which is also the correct shade of dark blue. Plastikote isanother paint brand, Royal Blue (1134) an acceptable color for '66 andlater.