Also I would like to know, are both axle tubes flattened on top just to the inside of the backing plates. It looks from the pictures like a 4 Pinion diff did you count and confirm? If it is the Heavy duty 4 Pinion like I suspect it has the stronger Nodular iron housing and you can confirm this by looking for a capitol N cast into the side or top of it. Also should have mentioned you can check the health of the locking mechanism by also putting it in gear if standard or park if an auto and raising both wheels off the ground and grabbing a tire and turning. If in good shape you wont be able to turn it unless your an animal.