Yes David you have it correct. The 265 is listed in the 1957 sales brochure as initial offering. The 283 debuted in 1957 so both engines were offered in that year only. Beginning in 1958 McKinnon standardized production in the Chevrolet orange colour for all Canadian Ponticac V8 engines. The Strato Six was still offered in a few different shades of green up to and including 1962.

Interesting side note here is that beginning in 1970 Pontiac and Chevrolet engines were intermixed in Canadian built Pontiacs. GM Canada did not standardize engine colour rather used Orange Chevy engines and Blue Pontiac engines in the cars. This gave rise to a unique Canadian Pontiac vernacular "You got a blue block under the hood?"

I refer to you another topic that I have researched and posted, once again please quote source and compiler if you use it, CLICK HERE.  While not specifically an engine colour topic it does illustrate the V8 engine colour for the years 1955, 56 and 57. I would also note that 1955 V8's have been found in a much more grey tone with green tints. I have personally seen an original in this colour  but was caught without my camera on that occassion and I have never seen that specific car again.