Even though a sealed bearing may fit the bore and spindle, it is not designed for wheel bearing use because there is no way to adjust the bearing preload and the wheel runout. I have been using Meritor wheel ends with sealed bearings for over 10 years. However, they require a special spindle, and If a bearing goes out, I have to replace the entire hub. I keep a spare new one on hand, but I have never had to use it. Some of the steering axles have logged over a million miles. Here is a link to Meritor's pre assembled wheel end.

http://www.meritorhvs.com/MeritorHVS_Documents/tp0251.pdf