The only real problem with the xbox is the clearance with the gpu and optical drive. The cpu has pretty much a bigger headrooom and would probably work with most cpu waterblocks. The gpu on the other hand, needs a custom waterblock that points the pipes horizontally rather than vertically to clear the optical drive.
After that, you could use almost any radiator and reservoir you want.
Pre-jasper and probably jasper units would benefit from this as it would minimize rrod possibility to nearly none.