My understanding is that it is "just" replacing the tail shaft and tailshaft housing. The problem is that you take the tailshaft out from inside the trans, so it's a complete teardown / rebuild, where all you are doing is replacing the tailshaft and housing.
The other way that most people seem to think is the best way to convert a 4WD trans to 2WD (or vice versa) is to sell the one you have and buy the one you need. I've never done it either way so I can't tell you what I think is best
Bob
Sorry, no '80 - '86 Ford trucks
"Oswald": 1997 F-250HD crew cab short box, 460, E4OD, 4.10 gears
"Pluto": 1971 Bronco, 302, NV3550 5 speed, Atlas 4.3:1 transfer case, 33" tires
"the motorhome": 2015 E-450-based 28' class C motorhome, 6.8L V-10
"the Dodge": 2007 Dodge 2500, 6.7L Cummins