231 is a part-time 4x4 only 2 high, 4 high, 4 low
242 is part-time/full-Time 2 high 4 high full time, 4 high part time, 4 low
I know you can interchange 231 and 242 if you get the correct spline count, not sure on the 249. You can rebuild your 249 or have someone else do it but it may be...