Here's a bit of insight of what I went though designing this:
For the stages I turned the shaft down to 3/8 round at the ends so when we used a round bearing they shaft would be sandwiched as stated above and stay in place, which worked out nicely since I didn't need to put in any eclips or collars. Also the 7/8 hex bearing has a very poor loading performance for this gearbox it would have been fine but in general getting good cheap 3/8 round bearings are easier.
The output shaft was also turned down to 3/8 round so I can interface it with our pully
https://sphotos-a.xx.fbcdn.net/hphot...84491030_n.jpg.
We don't have hex broaches [wish we did] so just using an set screw on a flat on the shaft was fast and easy. Also since this is mostly a low load application the set screw will be fine.
For our shooter we turned down a 3/8 hex shaft and milled in a key way so we could interface with the 3/8 AM Wheel hub.