Not sure where you can find a conversion kit. One of my LHS use to carry it but I went to their website and it was gone.
Also, to make it a "true" XR, you may want some of the upgrades, although in my opinion, not all are necessary. Aluminum center diff mount, full universals, torque rods, etc. All of these parts cost a lot and is not worth it to put on an RR.
I have a near brand new XR for sale. Let me know if you're interested.