You could simply make/get an adaptor to attach the drive shaft directly to the motor shaft without the use of a pinion/spur arrangement...
That sounds interesting...2 brushless outrunners back to back driving front and rear driveshafts via a coupler of some sort....you'd need two discreet esc's but why not ??
Why would you need two motors? Aren't there motors out there with shafts on both ends?
I don't honestly know.My exposure to outrunners is from the aircraft realm and none that I can think of have shafts exiting both ends long enough to couple to.???