The original 251's in the bombardiers were Canadian Industrials but since the every day truck and car engines fit in there so well you can find yourself with a totally different engine. I had what I thought was a 251 and was thinking about ordering rings for it. If you go into the Forums section of Allpar and go into pre 1960, you will see where some of us were attempting to identify our engines by engine numbers and casting numbers. Turns out mine was a 228 out of Fargo one ton made in 1949. There appears to be little difference in some of the engines. The ones in trucks generally had a T at the start of the engine number. The 251 and 265 are pretty much the same except the stoke is a bit longer in the 265. There is a plug in the head you can take out to measure the stroke if you can't find it by the numbers.