Nitro gear install

[AUS racer]

Anyone got a procedure on setting up and installing new gears into a Nitro Gearbox? I know there are shims in the gearbox that need to be added and taken out to get the correct preload, can anyone tell me to procedure on how to do this and where the shims are?

[AUS racer]

http://s3.postimg.org/i1q6tujlb/sst60_jpg.jpg (http://postimg.org/image/i1q6tujlb/)

Left is new gear from seaway right is removed gear, looks like there is a sleeve that somehow comes off the old gear and goes onto the new. I have also noticed the back of the new gear has a poor machined surface, its not suitable for a bearing to run on it. I'm guessing the sleeve comes off the old gear and that has a machined face on it that the bearing can then run on?
Anyone know what Im talking about?