2 different things. The 2-speed trans goes in place of a center diff. The 2-speed clutchbell goes in place of a standard clutchbell, or in our case for electric a Mod 1 pinion.
RC-Monster has a 2-speed pinion adapter that you would use with a 2-speed. You get the adapter and then choose the 2 gears to put on it.
http://www.rc-monster.com/proddetail...adapter&cat=40