What servos, reciever, and stamoing are on the motor?
It seems all the above, besides the HPI (no offense) seem likely. They all have the same bumper style, the top plate are the same shape with the on/off switch in the same spot. Exhaust seem Kyosho to me. The belts all run the same path, same "spur" by the motor.
Look at the hpi belt rs4 chassis vs this one. This is aggressive style and has sharper points. Hpi also tends to cover the bottom diffs with the aluminum chassis.