Well,I'm no expert, and I haven't even really built one of these trucks.
Damn, I did forget about the NP203. The np203 fulltime case came out in 73, and was only available behind automatics. I don't think it was until 76 that ALL automatics had that case though. There were three different output shaft spline counts used on the three different transmissions available. The 10 spline, 27 spline, and the 32 spline. The NP205 can be found laying in junkyards with any of the three, so it can be assumed that that Tcase was available with all three....but you know what they say about assumptions.
88wrangles if you've got an np203 and 44s being powered by a big block....ouch!!! Keep a spare drivechain handy.
I think the better engine crossmember came out in 85, but again I'm probably wrong. If yours breaks, fix it. It has probably already broken and been repaired with that setup. The steering box mount is not so obvious and is often overlooked until the box gets ripped from the frame.
Never heard of an np206. What are the specs and what years was it used?
Also, that is a full-floating rear axle. It's been awhile, but I don't think the drums just fall off when the wheel is removed. It's similar to the front setup. PM redrooster, he's running that rear axle in his CJ.