You are probably best off finding a really really good alfa mechanic to do this. The cost of the bearings is not the issue. Setting up the bearing shims and preloads is really important, and without the alfa specialty tools is really hard. It can be done with the classic red lead to examine tooth contact, and micro torque wrenches to measure the preloads, but you really need to know what you are doing.
Doing it wrong can make for unbearable noise in the diff, and lifetime of months or less.
Robert
Doing it wrong can make for unbearable noise in the diff, and lifetime of months or less.
Robert