It must be the Aero chassis, because the WS 750 had a front engine. What baffles me is that it looks as if the chain drive is connected to the left rear wheel. Rosellen writes that the right rear wheel was the only driven wheel. Perhaps it is the first chassis, as Rosellen writes about difficulties wth the gearbox which resulted in a repositioning. The chassis picture looks as if the stickshift protrudes to the left of the driver, a detail not visible on later pictures.