The 920 is designed for solid towing, so it's a bit more gearing, but way better steering. (I had to rhyme). You can put a box on anything, with enough time and materials, maybe a little patience. All the older series trucks ARE going to be uncomfortable for long trips unless you start changing out cab seats, add sound proofing, etc. The 920 I'm told is better than the m109a4 or the 934.
Yep, 6 wheel drive, except the 920 is 6 wheel drive with the helper axle not. Do I detect a Sand Dweller? If so, I'd recommend super singles on your rig.