1930s US versus Canadian differentials

The 1930s Mechanical Procedure Manual in Section 13, page 10 has a note which says that the rear axle service procedures apply to Canadian built models, except that the differential "component parts are not interchangeable between United States and Canadian Production Rear Axles". This will affect owners of Canadian vehicles who want to participate in the ongoing gear ratio upgrade project. If anyone has any further insight into the differences, let me know. More research and examination of actual Canadian parts is what we will need to do. Also, we cannot be absolutely certain that a US car wouldn't have a CAN differential and vice versa, due to swaps, etc. But I would guess that to be a low probability.