Last year dad upgraded the track and skis on a used '11 xtx and surprised me at where he could take the thing. He did a 1.75" backcountry track with the Yamaha dual runner ski's. With the lack of track it actually was one heck of a tree riding sled. I'd do a 2" incase you get in to some insane powder, Yamaha mountain ski's, and while it's out I'd recommend changing the drivers out to some avid drivers so you can run a looser track. Like said above, just have to cut off the tunnel and heat exchanger protector.
For the track, I'd just call up tracks USA, usually have pretty good prices on tracks. Ski's either look in the swap meet for some take offs or go to your local Yamaha dealer.