It'll be somewhere along the line of a multi-stage gearbox powered by a CIM motor; no final location (stage-wise) was chosen since we're still looking to see if any good COTS differentials exist (and if they have speed/load limits). It will be used in a pretty harsh (non-drive train) environment, so a good factor of safety will be requirement. Further details are classified until ship date (or the vicinity thereof).
If none are available, we are looking at getting some 1/4" or 3/8" wall 6061 square box tubing, and milling the bearing/bushing holes into it, then face mounting one side of the box tubing to a dead axle'd gear or timing belt sprocket, with something that looks just like the stereotypical textbook differential:
Thanks for the link to the HPI Racing model (this was just the kind of thing I was looking for); I just sent them an email requesting additional information.