Yes it's the number of splines on the tranny output shaft (TC input) that is different. Abovetimberline says it correctly in post number 2.

 

So I've read through this post and am more confused than when I started...lol!
Can I get the simple answer in Barney terms so I can understand.
2001 XJ classic 2wd. If I can find the tail housing from a similar year XJ I can just swap housing for housing and bolt on the t-case? No mess, no fuss? I'd rather not pull my tranny and risk an unknown junkyard one since I know mine is fine.