[Captkaos]

sure it is your last question..
Yes, when your order the gears and the differential (carrier) that will be all you need. They will(should) match your gears with the carrier.

The differential (carrier) is different due to the size of the pinion getting smaller/larger base on the gear change. A 4.10:1 ratio has a MUCH smaller pinion gear diameter than a 3.07:1 ratio, so the carrier flange that the ring gear bolts to is posistioned closer to the centerline of the pinion to make up this difference.