ok the case arrived yesterday and i done the first test fit to see if my plan would work and it was almost perfect.
the posts in the case obstruct the board slightly for lying flat. but i think i can grind out 2mm off the board so that it fits snug.
stripped down my netgear wndr3300 and sat it on the case to give me a better idea of how it would fit and how much i would have to take off it and its a better fit than i expected.
so next step is trim the motherboard so it sits flat then trim the router so it fits on to the bottom of the case and fit the antennas.