Are you talking new or used gears?
If used find out what the shims under the inner pinion bearing is and start with that thickness.
As for the carrier bearings take the old ones off and hone them out so they slide on an off and use them for setup. Then after you get everything to spec, pull it apart and press on the new bearing and recheck that everything is in spec.
If new gears see if there is a number scribed on the end of the pinion. If so that number is the distance from the back of the pinion to the center of the carrier. If that is the case, hone out a used inner pinion bearing for setup. Use a pushrod across the carrier saddles as the centerline of the carrier to measure the pinion setting.
Personally I would not run 3.54s on a spool unless I wanted to break stuff.