Part time 4x4 to full time 4x4 conversion kits?

Are there any relatively inexpensive solutions for changing an 96' jeep cherokee with part time 4 wheel drive, to full time?|||You have the Command-Trac (NP231) transfer case which is a part time transfer case only transfer case. You need a Selec-Trac transfer case (NP242) which is part time OR Full time. So basically you need a new NP242 transfer case.|||In addition, the different transfer cases may require different drive shaft lengths.|||While this is not that difficult but you do need to know what the input splines are because an older cherokee NV241(slec trac) I believe is a 21 spline while the newer ones off liberties have the 23 Spline, The clutch packs they put in the NV241 on older ones could have gone to crap so I would be sorta careful if you go cheap and buy from a junkyard! you should not need a longer driveshaft for this installation as the NV241 is not much bigger then the NV231