has been done, i was pretty much on track to do a 13bt but couldnt find any clean cuts for anything less than an arm and a leg, but from memory, if you use a 12a front housing, its heaps easier to mount, and if you use a s4 gear box, it should pretty much come out in the right place. A friend of mine recently completed a 12a conversion, I had pics but they are lost in my old pms, but there is one fellow floating around here somewhere, might have not made a new members ride on the new site but he had a pretty clean example.