u can fit the other tranny, u cant fit genesis spur gears without the alloy hubs that come with it, they may be available seperatly instead of the whole kit, not sure if the bearings are a straight swap tho... but anyway, its listed on cens site as an option part i think, it used to be there somewhere - just be sure to get the one with the right shaft, theres 3 types iirc - u want the shortest one