Great news, Neely! Isn't it nice how things tend to work themselves out, sometimes?
Don't worry about the top end on the KDX, it should go smoothly. The biggest problem I had with the first top end on my KDX was all the carbon build up in the KIPS valves. It was a real bear. Had to take it in to the mechanic, and HE even had trouble with it. But, he eventually got the flapper valve out, and everything cleaned up and went back together very nicely.
Periodic maintenance of the KIPS valve is necessary. The second time we took it apart, it was much easier. Get a service manual for the bike, if you don't already have one. With that, and some help and support from my better half, doing a top end was a great learning experience.
Enjoy! You'll love the bike. It's a "four-stroke lover's two stroke". (But with easier starting and better suspension than your XR! :D )