Shimming takes time. There are several different ways to do it. Look on youtube, there are several really good video's on this. You will be opening and closing the gearbox several times to do this correctly. You can get really good results by shimming with the motor.
As far as the rear wire from a front wire gun, that shouldn't really be that hard. You just need to re-route your wires. You will need to make them longer also, and only solder them, don't use any electric tape or auto crimps to do this. Look online for video's showing open gearboxes and just look how the wires are ran. They are very simple.