Np-242 t-case question

I've been curious to know if the 242 tranfer case is the same exact unit from 87 on to 01? Have they made any changes in them since they started putting them in the XJ's?The reason I ask is I just got an 88 Limited XJ and it has the 242 in it and my 01 XJ has the 231. I would really like to put a 242 in my 01 and I was thinking about swapping them out. Would it be a direct swap? I would probably need to have it rebuilt, i don't know, but i kindof worry about an old unit like that. any help would be appreciated, thanks