First off there are many rotors that fit into other stators, I have done it myself just to experiment with my dyno and motolyser, but according to roar you are not allowed to Frankenstein the motors. They all have to be parts from one manufacturer.
Also closest to the sensor board doesn't mean you will make the most power.
The best that I have found is to use a fantom facts 3 that reads how strong the magnetic field is, Mark on the rotor where the strongest readings are (usually is center of the rotor) and use the shims to get that point to the center of the stator.