To help position the horn, apply a strip of double sided tape to the horn base and then place it on the rudder/elevator. This will allow you to fit the pushrod and make any adjustments in the position of the horn without ruining the rudder by drilling holes in it. When you are satisfied with the posioning, drill the mounting holes, remove the horn and take off the tape. You can fasten the horn with the screws and it will be exactly in the right place.

Wedge