I got the sideplates milled out and attached the gears to the shafts yesterday using roll pins (spring pins). A few of them are too long and keep binding against other gears so I plan on grinding them down. Otherwise, they were very easy to use.
If anyone else plans to use roll pins, I would definitely recommend getting a roll pin punch like this one:
http://www.grainger.com/Grainger/items/1Q760
It makes insertion a million times easier and prevents the tip of the rollpin from spreading out from the hammer. I had someone gently hold the pin with a needle nose pliers and put the punch on the pin and hit it with a hammer. It went in without any problems whatsoever each time. Without the punch I ended up bending a few pins.
thanks, Vivek
EDIT: thanks for all the information on e-clips, I will definitely use them in some of my other projects. I bet we could save a pound or two by replacing shaft collars with them!