That Eaton unit is a great piece. Even with the 3:42's that could be a good set up and should get great mileage.
I am thinking of using one of these:
http://www.rockauto.com/Newsletter/a.../10-16-14.html
The Spartan Locker for my '85 10 bolt is Part # SLGM8528. At RockAuto.com it is $292.79. I can do this install myself, because you out it in the existing carrier in the rearend. just have to keep track of the shims for each side when you pull out the carrier. Bearings and Races can be replaced and should not effect the shim pack.
Just another way to think about it.