I think the design and parts used depend on what pedal assembly you have. Mine came with the Tilton pedals and looks like the attached. In the first picture, the small plate stamped "SLC" is the one used - the other plate is not used (must be for a different pedal assembly?)
The allen head bolt needs to be pulled up all the way into the shoulder fitting in order to clear the lower plate.
On mine, I found that screwing the shoulder fitting out just a bit would allow the allen head bolt to clear the hole. I did have to grind down the outer diameter of the allen head a bit so that it would slide in and out of the shoulder fitting a little better.
I know some guys prefer to mount their slider with the pin at the top of the pedal assembly, as they find that it interferes with their foot. On mine, I found that my heel is well back from the base of the pedal when sitting in the car, so I left it with the pin at the bottom where it can more easily be reached when mounted in the car.