I got mine today and have been playing with it a bit. The good news is that the new bulkheads will fit all older models no problem. The single speed tranny is in the exact same case as the X, so it will bolt right in too.
The diff ring and pinion are new and look tough as nails. The bearing on the ring side is now larger so it should hold up better.
The trans has a new primary gear and a new thicker idler shaft. Hopefully it will hold up well.
The motor mount is massive! Should clamp great.
I put on the optional 25 tooth pinion and will run it with two 3S 5000 Flightpowers. I also put on some stiffer springs on the big bore shocks. It comes with the pink spring (medium-soft). I used the white springs (medium-stiff).