973 has posted CADs of many of their recent robots. All their bots(except maybe 2009, don't remember) have shifters based off of supershifter parts. This is the best way of doing them because you can get most of the parts without having to machine much. To get aluminum gears check out WCP:
http://wcproducts.net/gears-20-dp/
On the topic of gearboxes, I highly reccommend you go COTs your first year of shifters. You don't want to run custom during the season if you haven't prototyped during the season. WCP is releasing some new shifting and nonshifting gearboxes that you might want to check out(WCD and Regular), but the supershifters are definitely a great, reliable option too.