It's the same as a trimble that I did last winter.  It had a bracket with little holes in it to mark the back side.  Make your own.  drill the hole you see and then make a piece of tin with a bend in it so you can match it perfectly to the other side.  You just measure up from a common point on the  elevator and you will have them the same hieght and the bend will make them the same depth.  You should also use a step bit to drill the holes as it will not grab the tin of the elevator.  They are also shorter so you can get in behind better if needed.  I needed a step bit and right angle drill to drill my back hole on my 1688.