You don't need that with the new slipperdiffs... the whole point of this early "slipperential" was to incorporate a (revo) slipper. You'd just need a simple mount to get the new slipperdiff into the gorilla chassis.
But I guess you know that.
I think Crazys point is that he needs a transmission, to follow some rules or whatever.
Edit: Yeah, something like V1 plus the new slipperdiff would do the trick. But not for CrazyJr I guess