I don't use a case spreader, I have a set of set up bearings and use them to determine on the carrier to get zero preload on those bearings and when I'm done setting up the gearset I remove them and press on the new bearings and add between .010 and .015 shim to the carrier shim packs to get the preload correct. I do set the backlash up before installing the new carrier bearings also
I set the carrier on the case with the bearing races angle into the case and tap it gently into place with a rubber or plastic mallet
Works good so far ( going on 30 gear set changes now)