Its common practice to replace the TT 40 bearings on a new engine if you plan to race them. The rear bearing will not last long at high rpm.

Not sure why anyone would completely break down an engine just after breakin. You can check the rear bearing by pulling off the backplate. Heck, I just found 2 rear bearing problems doing this (different manufacturer). The purpose of breakin is to get everything seated (including bearings), taking it apart messes that up. There is no way you will ever get everything back the way it was.