Since it seems to be a recurring topic, and I had to do one on my second hand Connie anyway.........
Rather than repost it all, just follow the link:
http://www.the-ashpit.com/mik/gear.html (http://www.the-ashpit.com/mik/gear.html)
Honestly, it isn't very difficult and doesn't take more than about 45 minutes -- as long as you're careful and don't have to play "hunt the screw" too much.
Great tutorial!
My only change would be to install the brake rigging and bottom plates BEFORE you attach the gear box. To be this was a lot easier as the drive axle was held in place.
Stan
Two suggestions:
1. Line the styro box piece with some soft cloth so you don't mar your paint if you use the piece for a loco cradle.
2. Use a magnetic screwdriver or put a small magnet on a screwdriver when you are taking the little ones out and don't want gravity to pull them into limbo in some inaccessible part of your loco.
-- D