I have Andrew's kit in my Iron Man. I have it set up to hit the side of the cabinet and it gives off a nice crisp and loud knock that is very similar to the old Bally/WMS knockers that were in the backbox. I initially set it up inside the cabinet as Data East did and as pictured above, but I wasn't happy with it as I felt it was too muffled.
I mounted mine at the lower right front of the cabinet to the right of the cash box. I put it there because there are no triangular bracing pieces that require you to raise the knocker off the cabinet floor. Plus it gives a great knock as it is right up front by the player. The wiring is long enough to do this if you are careful how you route it and where you place the control box. You do have to be careful when you fold down the head as it is right at the limits of the wiring's length.
You could probably mount it on the left side at the front and the wiring's length would be less of an issue, but I have a shaker motor in my IM and this wasn't an option.