That sounds easy enough, a wheel collar on the piston shaft then.

Zetti, to elaborate, there is a lot of discussion in this thread about the thrustline of the turbine and how it affects the Hawks handling. Placing the turbine above the rails (aircraft upright) angles the thrust line slightly down compared to mounting it below the rails. This offsets the Hawks tendency to pitch up during high thrust acceleration. The limit of how far you can move the turbine is when the thrust tube contacts the elevator servo mounting plate. But just mounting on the top of the rails is not a problem.