[ptitchener]

I would suggest that you sould consider using a much larger gear reduction on the motor. A CIM with only a gear ratio of 12.75:1 will not have enough torque to lift an arm that weights more than 4 pounds (according to the JVN mechanical design calculator). Worse than that, even if you do make your arm that light, then the motor will be going so rapidly that your arm will spin nearly as rapidly as the wheels on your robot. This will make it so that your arm will be totally uncontrolable and possibly damage your robot. If you use a 12:96 sprocket reduction out of the toughbox, then you should be able to lift the arm, but it would still move very rapidly. (you can get a 96 tooth sprocket at VEXpro)
If you are certain that you want to use the CIMs, then the GEM planetary from AndyMark would probably be the best idea. Otherwise, you could use a different motor with a larger reduction gearbox that you already have or you could try to make your pneumatics legal.