The 231 is supposed to be stronger and there is more aftermarket support for it-sye-lower gears etc but I have about 10 months on my junkyard 242 swap with no problems and it sure is nice having the fulltime setting for daily driving in the snow around town. I had get "creative" when I did my swap due to the input gear being a different cut than my 249-used the 249 front case with the back half and internals from the 242 xj case that I used but it works fine.