The bearing is shorter. The gear floor is almost twice as thick around the outside. This is the area where the gear usually fails. All bravo drives starting with 0M serial number have the thicker gears.
The teeth on the XR gears are forged directly to the finshed shape. This makes for much better metalurgey and a stronger gear. The Bravo lower gears have always been net forged.
The net forging process allows the addition of reenforcing at both ends of the gear tooth. This just about eliminates fatigue of the tooth.