http://techon.nikkeibp.co.jp/english/NEWS_EN/20110724/193591/?SS=imgview_e&FD=47620101
The other thread you might look at is
Hot-rodding the Toyota MGR. The OP, e*clipse, is working on combining two of the MGR in a custom case. It's rotor splines onto the shaft. He might be interested in or have answers to your questions.
Arcimoto use two electric motors in front-wheel drive. It's not clear to me if there is a differential or the controller[s] provide the differential action, driving each wheel separately.
To what will you custom shaft connect. IOW base vehicle, front or rear drive, lateral or longitudinal, etc. Have you considered putting one MGR on each end of the car for 4WD?