Xterra's and Frontier's use different length rear shocks, so do your research. While these will mount to either vehicle, make sure you know what you are getting and the results that you will get by installing these shocks. Compare the posted lengths to confirm they will provide you the correct travel for your application.
Xterra's use 1" shorter rear shocks. Example - Bilstien p/n 6252 installed on a Frontier is used for 0 - 1" lift but on an Xterra the same shock is for 1" - 2" lift applications (source PRG).
I discovered this when I swapped my suspension from my Frontier to my X.
I never researched DirtKurt's setup here. When I bought them, I knew they were originally bought for a frontier. They've worked flawlessly for me. I did have them serviced about a year ago. There is no leaks. The seals, bushings and pistons are in great shape.
I'm happy to answer anyone's specific questions. Yesterday, I called and spoke with Nicholas at King regarding someone's specific questions. I'm happy to help however I can