technically you need a dial indicator to set back lash. i doubt that the factory settings had no shims in there, but yes you can re install them with the current shims. one thing you must do though is to take the pinion bearing off and take out the shim that is inbetween the bearing and pinion. put that shim on the new pinion and install a new bearing. (press to remove, and hammer on the new one) most likely the pinion shim will be ok, the ones you need to adjust for backlash are the carrier shims thickness. you should install the old ones and mark the gear with gear marking compound, and feel for backlash, as an inital reading. then go from there.