one other point that will probably fix the rudder pushrod, after you've set the endpoints (the servo travel and subtrim) you'll very likely need to mechanically re-adjust all the flight controls...
Sub trim will cause the servo to center in a different spot, and I'd bet the rudder pushrod will miraculously 'grow' to a more correct length.
if it doesn't, is it possible the rudder servo is installed backwards? (backwards specific to this model, there isn't a rule of thumb with the servo's control horn further away from the rudder rather than closer to the rudder)