the only thing you would need to do is weld on a rectangular aluminum tab onto the newer swing arm that matches the the groove in the hub on the drum. Also there was a post awhile back on a flat track with custom disc set up. I think he used a (exspensive) aftrermarket cush hub. Not 100% sure on this, so don't quote me.
My Xl is mostly for hitting the trails so the cush is not overly important to me. If I am doing an adventure ride and loaded down, I probably won't be doing power wheelies anyways.