Looked at HPIs site in japan on the Savage 5T according to the dimensions its actually slightly narrower than the XL and X
So in all truth from what I see the only thing needed to convert a X or XL over would be the Bajas tires, the longer TVPs, a longer wire for the throttle control, and the one drive shaft.
Currently I'm getting the japanese manual to see what else is different part # wise but the japanese site is slow as hell.
(edited to upload the 5t's parts list)