There are problems when fitting tapered roller bearings in the front. It can be done, but the inner bearing races need to be radiused to clear the radius filet from the spindle to the upright. The same problem also exists with the original type ball thrust bearings that are now being produced. Several people have spend a great deal of time researching this issue and the results of their work is pulblished on the MG Experience site. http://www.mgexperience.net/article/mg-midget-wheel-bearings.html
When using tapered roller bearings the spacer is not used! That type of bearing must be adjusted differently than the thrust ball type bearing which needs the spacer to prevent applying too much side load to the bearing.
I've not heard of any problems with broken stub axles except for cars involved in racing running slicks and pulling high g's. I've run tapered roller bearings on my car for several years now without problems and run 205-60-13s on 7" rims with some very sticky Yokahama AO48s.
'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8
"There is a fine line between a hobby and mental illness"