We've used Martin Gears' HM1616 (16 teeth, 16 Diametrical Pitch) miter gears for the last 2 years, but will probably switch to M1616 (not hardened) if we do this again. Gears have 3/8" unfinished bores. We cut our own keyways (finished bore gears are too expensive). We've had good experience with these.
Here's a view of our 2011 Pivot Module. Our Module includes the motors and angle sensor:
http://wiki.team1640.com/index.php?t..._annotated.jpg
Mass is 9.1 lb including motors, gearbox & sensor.