The Power Wagon is a 1956, that had a flathead 6. Had I known what I know now, I would have replaced the axles with Dana's and been done with it.What year is your Power Wagon, is it one of the old ones that came with a Dodge flathead 6, or a modern one? If an old one, a married 205 with a centered diff. would be a lot stronger and one less driveshaft. Of course need to replace the axle. Also, do you have enough wheelbase for two driveshafts?
The only vehicles I recall that used a np200 were the old power wagons and the Kaiser built m715( possibly some jeep gladiators ) Check with the Power Wagon crowd. I have a 56 pw also. I used an 86 f350/250 single rear with IH 205 transfer. The 200 offset rear can give a bit of gear noise though it may not be as noticeable with a diesel.