So here's my question. I have a 2000 xj with the 4.0L auto tranny NP231 tranfer case. What 4.0 are interchangable with mine. I plan to buy one and rebuild it for a back up. just don't want to buy one that won't work. Thanks everyone.

 

The block has remained the same,the heads have changed first in 91 and again in 99,I am going to be rebuilding my spare motor soon,It will be a short block and when mine does go out I will just rebuild the head,I am still not clear on the 99 head and if the intake and exhaust will bolt up to the earlier heads. I do know the gaskets are different.