I run this CB
http://www2.towerhobbies.com/cgi-bin...?&I=LXM729&P=7
and I run either 52/49 or 49/46 gearing with the .18 CV-R.
If you do want to use that clutch bell that comes with the 2 speed you will probably have to get the gold pinions which I think are 17/21 and probably have to run 52/49 spurs. I'm not sure the slots in the chassis are big enough to let you adjust the gear mesh though. I'm also not sure how much acceleration you will have. Top end will be crazy though if the motor has enough umph to get it up there.
Also a warning, the 2 speed has no slipper. When your clutch shoes are expanded and connected to the clutch bell EVERYTHING is connected. Just take that into consideration if you go off road or jump it.