I just did a NV3550 conversion on my 88 YJ with the 4.2L. Just had to change the bell housing and a new slave cylinder for the clutch. Went in pretty easy. Did you ever pop under and look for the tag to see what kind you have? If you got a 4.0L from a cherokee you might have an AX15 in there already..in that case just find a new one, they're easy to come by.