I doubt that any bearing on a cub cadet is proprietary to IHC other than the plastic bushing on the steering shaft
You are certainly free to believe what you want, and maybe one of these early IH part numbers can be crossed to a bearing that can be used: ST 435, or IH-391237-R91. The only one of the bearing's I have out right now is marked PHC 217 W1B, or it may be an 8 rather than a B, so that may cross to a usable replacement. The ID, or bore of the bearing's, is 5/8".