zeos,
Are you talking about the plans for the Namco style cab, or this Tron cab?
In the Tron cab, the monitor shelf is at about 6" from the bottom.
In the Namco cabs, the top edge of the monitor shelf sits at 7", see diagram below. If you can , you might place the monitor shelf intentionally a little low (by a 1/2" or so), and then you can always fine tune by simply adding a spacer.