I would think that you should focus on the bearing preload, by meassuring the backlash between the pinion and the crown, otherwise you will risk wearing the pinion or crown if too much clearance ($$ at worse) or burning the bearing if you don't have enough clearance..
Please note that this is just IMHO, as I am not an expert by any means... however I am telling you this because I have previouslt ruined both... (non P cars)..
Good Luck
PS: as you know, you adjust the preload with different shim thickness