I am glad that you didn't have any issue with it, but if I understand correctly that you are forcing the Futaba wheel on a JR output shaft, then I have to strongly caution against anyone else doing this. Putting a Futaba arm on a JR output shaft will lead to stress cracks and eventual failure.
As for running the JR servo arms- the best to use are the JR arms that have the metal sleeve that reinforces the area around the servo output shaft (splined).
Almost all of the machines I have looked at with JR servos have the carbon plates mounted on the outside of the servo arm, which alleviates the interference with the top of the servo case, but makes the control rods canted out at an angle. If you want the geometry as Matt intended it, you need to have a very shallow head on the screws you use to mount the carbon plate.