Another question that needs research (by me)!
Chervolet # 13 Can production may have started with 1942 Models, serial # 284XX0001. Prototype C8A HUP # 284450006 was supposedly built in February 1942 but it has an earlier, 1941 Model engine. I have to suggest that the evidence for Oshawa plant is therefore 'from February' or perhaps March, 1942.
As regards Windsor, I have no information save that there is a photo in one of Dr Gregg's books of the plant with # 12 and # 13 cab trucks which was at the change-over. demand S/M 2126 and 2127 were for C60S and F60S trucks for Australia, and included both # 12 and # 13 cabs I gather. One to 2126 was assembled in September 1942. I can only suggest that Australian production was a few months later than Canadian.