Every kit will be slightly different. You could end up with shims on both sides, or just on the gear side. On the front diff, shim it like normal to where you end up with slight play between the ring and pinion when it is assembled in the car. On the rear, shim it tight. No play. You might also need to put a shim behind the pinion to push it a little closer to the ring gear. I used KYO96644 for that. One shim between the pinion and the bearing.