Gears
No the gears are not interchangable, but the complete diff assembly is, but you will need new ubolts, and c bolt plates. As far as the front rotors are concerned you will need new bearings, and rotors from a 2wd expedition.
You would have to swap out the entire rear axel hub to hub. The 8.8 rear axel has smaller tubes do you need the correct u bolts. They are cheap to have bent up so just replace them don't re use u bolts

