general SYE question

A friend of mine ordered a RE 5.5 long arm kit for his tj and ordered an Advance Adapters sye at the same time. some how he was shipped two of them and only got charged for one. GREAT RIGHT!!!
Well i read the whole installation manual and it said the sye's are the same for my cherokee and his wrangler. there is some vacum thing on a cherokee that the wrangler dosnt use, it has a plug that may be installed on his jeep. but it seems as if it is there for mine. Now even though i read the words myself, about it fitting my jeep. another friend of mine that did an sye on is tj, swears it will not work on my jeep. i have done the best i can to research it further, and now i dont know whos right.
mine is a 1990 4 door limited
does any one have anything they can offer, cause i am going to get it for 150 bucks if it works. and i want it to work.

the NP 231 transfer case that is used in the majority of modern Jeeps are the same internally so if you have the 231 it will work for you. i see you have a Limited, and that may be an indicator why your friend says you cant use it. alot of Limiteds came with a "full-time" transfer case, the NP 242, easy way to tell would be if your transfer case shifter has a FULL TIME position, in addtion to the standard 2hi, 4 hi, N, and 4 lo... the 231 does not have this FULL TIME selection.
242 and 231 are very similar and i've heard the SYE kit can work with modification but for practical purposes it wont work.
identify your transfer case and you'll have your answer.

thanks man that helps bunches!!!