Locking hubs, manual or auto, disconnect the front wheels from the axle shafts.
That way, when you are in 2WD the front axle shafts and drive shaft do not turn. This results in less wear and tear on the front drive train, and better mileage.
You should just be able to swap the hubs in place of the ADD drive flanges. You could replace all the ADD parts with earlier non-ADD stuff, but it may not be worth it.