[rotorwrench]

That should be a C51A block unless it's a prewar C81A casting. They made them for a while after the war but we seldom hear much about them. I don't think the prewar Canadian blocks had the raised casting numbers on the front of the block like they did on the post war C59A and C69A blocks. It would be interesting to know if it has a raised casting ID on there.

The US designation was 41A for the post war 221 blocks and they had many characteristics of the prewar 81A block but most have the 59 on the bell. I think they used pewar type sand cores from the old engines inside the core boxes for the 59 series blocks for production casting. How they could ID them at the factory before painting is a mystery to me. You have to know the characteristics to tell them apart.