[Brian]

"Canada kept building the 81A engines pretty much the same before and during the war as far as I know. They didn't have time to do some of the changes that were done here in the US".


I disagree with this statement....The Canadians implemented many changes that the USA engines never had, eg shell bearings, the oil filter... Also, as I stated in my above post, all the civilian blocks had cast in identifying numbers, ie 81A, 91A,99A,01A,09A, etc, right through to the end...Exception being the military blocks.
The one sticky point is the 81A blocks...the first of them ran the earlier short snout, small journal crank, and yet the blocks still have the same number as the later, large journal 81A blox.