Kevin,

I'm afraid I can't help with your question but why is it that important that the servo be compatible with Futaba splines? Can't you simply use the servos arm and adjust for the needed throw with the arm holes?

Also note that modern retract servos such as Spektrums are proportional as opposed to 180 degree. They allows you to more easily attach the pushrods at the ends of the arm and "dial down" the servo until appropriate throw is achieved. Also, if you plan to use two servos in a trike setup, the NG doesn't require a 180 degree retract servo - a mini will do the trick.

David