Don't like to dampen ideas, but I think you have a problem. It will fly apart. A full scale LeRhone turned how many rpm? 2400? If you spin up a glued together plastic model on your engine it will not last long. And even if you could keep it together, you would end up with a huge torque reaction.

What might work is to install ball bearings inside the Williams engine and let it freewheel behind the spinning prop. Creatively add some "baffles" that act as a prop and the motor will spin. And hopefully not fly apart.