Mine arrived last night and it comes with a new slim chassis, new motor mount (more centrally located), new diff halves with keyed diff plates and 39t pulleys also longer drive belts and (presumably) the 502X battery mounting plastic parts.
Think that's it apart from a few odd screws and spacers.
Of course i'm assuming that by putting all this on the car I will become a world champion and all for a shade over £100. Bargain!