Owen,
I think you might be right that the steering box could be of a cab13 C15, but don't have the info to confirm for sure. I did check pictures of 3 (early 1940) Cab11 C15's and they all have the same steering box, which is different from yours.
Regarding bearings....Cross reference websites can be a great help. It seems the bearing is also used in a number of tractors, which might help in finding a replacement bearing closer to home.
https://www.yoyopart.com/oem/1045933...co-10983r.html
Alex