I got my heavy duty Adjustable control horn set from DU-BRO
I changed from what the kit manufacture sent, that plastic stuff that is okay for smaller models
I first laid out some green tape for marking purpose I laid a piece of wire there to get basic line up than I put part of the control horn assembly as a reference point started to measure everything
I had to make sure when drilling the hole it was at a right angle to the center line of the control surface
I used a couple of clamps to hold the aileron steady

always measure twice and cut once