I'm not 100% positive if I'm gonna remember all this correctly since its been a while since I did all the research for the 247-->231 swap. I'm pretty sure it has to be a 95+ model because of the gear cut or something like that. I'm also pretty sure it needs to be from a 6 cylinder power plant because of the spline count if I remember correctly. Both the 247 and the 231 have 23 spline inputs however the 231s standard input shaft is to short for the 545RFE tranny. So once you pull the 247 you have to tear it and the 231 apart and swap the 247s input into the 231 case (its a direct swap). You'll also need to fabricate a new linkage setup because the 247s shifter linkage won't go through the entire gear range on the 231. There might be a way to do the swap without doin an SYE of some sort but I don't really see why you would. I think someone told me there's a way to modify the WJ rear drive shaft to work with the 231 but I went a head and had a multiple double cardan shaft made. I prolly left something important out so feel free to ask me any questions and I'm gonna try to find the links the helped me through the swap.
Broke College Kid
99 V8 WJ ---> NP231 w/sye, 4.5" (KOR Lift) , 285/75/R16 Maxxis Bighorns, Front & Rear Woody Shafts, Kolak exhaust w/FM50, K&N FIPK, CB, KOR Rack w/Daylighters, Aussie Locked D44a
Future Mods: Sliders, Homebrew Long-Arm, Front Aussie Locker, Homebrew Bumper with Winch