7.25 axle splines

If I understand correctly. You should be able to take the good differential Carrier (cage) out of the one rear, and swap it into the rear that has the bad unit. Keep your original ring and pinion gears. Just swap the carrier unit. You might have to adjust the gear back lash, either by reseting the adjusters, or changing shims (depending on the rear). Then use your original axles and brakes.