Trying to modify the NW radio box is a waste of time,it's pretty flimsy to begin with and with
a stronger servo you wind up ripping the screws out of the top,also the double linkages are a real pain
I've posted a picture of the Vision Sail radio tray before it's installed in the boat (I hope you don't mind Brian) It's a nice setup,uses two small cable's to control the rudder.
In another picture if you look at the on/off switch,this is where the rudder push rod came through the way I originally had the boat set up.
I know this site isn't about NW's but ther's a lot of good idea's on it,they modify a Victoria step by step for racing you might find something you can use on it
Sorry if the pictures are'nt the greatest they really lose somethig when I upload them