Bill - Here's a fairly recent thread on
ID'ing Canadian GMC engines that might help shed a little light on the subject. It too references a "C" engine serial number in a Canadian 1951 GMC that sounds like a Chevy engine. Can your friend provide the casting numbers from the block and head? There seems to be a little more info available on the casting numbers to better define the engine, than the serial numbers.
I was the recipient of your 1955-57 and partial 1958-60 Canadian Chevy/GMC parts books, which I am most grateful for! I looked at them yest6erday when your topic came up, but couldn't find anything directly related to the engine number starting with a C. The info in those books is only showing how to decode the truck serial number.
