The JR 6 channel radio, at least the 642, will not properly mix 2 elevator channels because you cant couple the trim settings, ie when you try to trim out the elevator, only one elevator half will move. I bet the 662 is the same. If so, you are better off with the Y harness. Make sure the servo arms are perpendicular to the push rod at neutral on both sides. 8 channel radios have the programming to mix 2 elevator servos, Futaba calls it Ailevator.

Peter