I'm not sure if it's just a tail housing swap on that or more. I think with an AW-4 it's more.
On my 44RE it's the whole rear extension housing including overdrive - but it's just 6-8 bolts and some RTV, can be swapped in half an hour in the truck ignoring shafts and tcase
I'll take the 2wd front axle if you decide to turn it into 4wd.