For reference our 3d printed ABS plastic ball lock transmission (as shown here less CIM) is 26 ounces.
The only metal parts are two 1" bearings, three thrust bearings, air cylinder, a few bolts and a precision 1/4" shaft.
http://www.chiefdelphi.com/media/photos/36161
It is possible to make a 1 pound transmission, but will it hold up?
Are you direct driving a wheel?
What are you using to shift?