The 55-57 Canadian Pontiacs had the staggered valve cover holes with a pontiac script in written letters. The correct colour is the question. Grey or dark blue definately not chevrolet orange. If the 57 Laurentian convert. that is featured at the coming RM auction is correct it is a blueish grey.
Not an expert here but I have posted on this topic before. I can only say what I've seen.
The brochure colour is pretty close to the 261 but the 265/283 engines I have seen in original paint are darker colour green moving toward greyish blue tones. The word Pontiac is on each valve cover in black. (I have seen similar script on post 57 orange engines too in black with an arrowhead emblem ahead of the P. The latest I've seen is a 64.)
One thing for sure is the tri five CP's are not orange and the Pontiac script is black.