BaldEagel

The first thing to do is dertermine if your wing/tail/rudder structure can take the extra width of two horns within the original horn mounting block, if you shine a bright light behind the moving surface you should be able to see the horn fixing block through the wing surface, lightly mark this with a soft pencil or water based marker, from this you should be able to make up your own mind if the fixing block is big enough, if not there are various ways to increase the area, which I will go into later.

Next is to determine the position of the dual horns on the surface, for this you need to have your servo horns sorted and preferably the servo in its final position, you will aslo need to know if you are going to use ball joints or clevis to connect to your servo's this will determine the line of the push rod and the positioning of the dual horns on the surface, although a ball joint will accomadate some misalignement, this error is so small I consider it worth ignoring for the convenience of using the original slot for fixing the horn in a composite surface.

Mike