One of my mates is upgrading to an Atlas and Currie diffs he offered me first refusal on his NP231 case with Heavy duty SYE and double cardin shafts. His TJ is an 04 manual D44 rear & mine is a 97 auto D44 rear. I have had conflicting advise on what is required to swap thm over obviously I will need to check shaft lenghts but need to know if the input shafts are the same and if the front of the case (where it attaches to gearbox/auto) is the same or would I have to split the cases and swap bits from one to another is there anything else I should have thaught of.

IIRC, there's no difference in the cases as long as they're both behind 6cyl motors. I do believe there's some differences in the linkage but that easily swaped from one case to the other.

They are both 23 spline input, but the auto has a shorter shaft. About 1/4" IIRC. And as stated the linkage is different, but easily swapped. The bolt pattern on the cases are the same.

Driveshaft length will change front and rear.

Paul

You can interchange an auto case with a manual case. In any case what really matters is the input spline count. His may be 23 and yours may be 21. And correct me if I'm wrong the linkage should be adjustable.

I do believe that the autos have a different clocking but its just a few degrees. It might stick down a little bit more but, i think it changed from year to year

http://www.novak-adapt.com/knowledge/np231.htm

Scroll down.

Paul