Here is the NSK part number directly off of the bearing I removed from a B13 intergalactic racing pony:
I can not find a bearing in the NSK catalog that matches the dimensions of this bearing. I believe it was custom made for the VLSD boxes for Nissan. That would explain the high cost ($185, dealer only).
You DO NOT have to remove this bearing from the diff to install the MFactory unit. You only need to remove the party from the intergalactic racing pony case to shim the diff to set preload. You should be able to do this without damaging the party, so there is no need to purchase this bearing unless it has gone bad.