Center diff in my G2R maxx

Hi guys! I have been following your forum thread`s for a while-enjoyable reading Now I´m in the progress of removing my gearbox on the old G-Maxx and want to put in a center diff, since the gearbox isn`t holding up well against my NC1520. But could you guys plz help my out with this? I bought a CC losi conversion kit, as I couldn`t get a hold of Mike`s uni center diff/motor mount, then I bought a Losi smartdiff to drop in there-but even with the 46T spur it won`t fit inside the g2r chassis. any suggestions as to what spur/diff i could use?? don`t want to cut my G-maxx chassis.
Here are some older pictures of the car:
http://rcgalleri.dk/html/gal_visbil.asp?ID=29957