I do it the way I described. I've done hundreds of gear boxes that way. Just put it together like you mean it and see what you have. Take it all apart and put it back together the same way. Keep everything very clean. I've worked with hundreds of journeymen machine repairmen, like myself, and we all use punchs or chisels to remove bearings from shafts. Of course we use a hand press when available but it's not necessary. You walk the bearing off the shaft tapping it on either side, alternating. If you haven't done this(walk a bearing off a shaft) before then maybe you should consider some hands on help for that part. You could take the pinion assembly down to a shop and have them 'unstack' and 'restack' on the new pinion.