So tempting...!!

Leopards

Granted I don't know much about the old Tamiya single motor drives..

Very tempting.

That drive train looks like a real battery killer if the servo is used to push the brake one track drive shaft or the other in order to turn all the while the motor continues drawing amps .

I remember a great video that showed it working, but haven't been able to find it in a while. I like the idea, its more scale and realistic to 'actual' tank transmissions. You get the jerkiness of a real take (with brake differentials) when you turn. I'll hunt down the video.