[Kevan]

I wish Sloting Plus would go to the next stage.
An example below of a torque tube from a 1980s 1/12th rc 
Lexan chassis from this era were extremely flexible. 
The torque tube design adopted by all lexan monocoque designs of the time. 

Locking the motor to the axle eliminates flex. 

That looks like an original Phantom 1/12th.  They were great years ('81-'83) but the advent of carpet killed off lexan chassis.  The torque tube was still used for a short while until dampers started appearing.