By having the same surface area on each side if the center of mass' X axis should give yaw without roll. May have to be the two surface areas sub-divided into smaller areas and then each sub area multiplied by the length of the arm from center of mass to center of sub area. 

There is no input from lateral cyclic to the tail at this point. It would unload the rotor controls a little. It could be considered at a later time. 

Ruddervator arm length is 12.73"

30º of movement = 12.73 /sin 30 = 6.365"

90º of movement = (pi * 12.73 * 2) / 4 = 20" of movement. 

If pulley on ruddervator is 3" diameter and movement is to be +/- 30 degrees (total of 60 degrees) then the cable movement must = 3" * pi * (30/360) = 0.7857" (total of 1.5714")