Just an alert as I'm a new builder and started by first build last night.
After doing a lot of research I thought I was good to go and had picked the Arctic Cooling Freezer 7 Pro to go with my Asus P5Q Deluxe.
Basically what you'll find here was confirmed when I tried to do it.
I had the same issue with putting it on my DFI ICFX3200. I cut off a little of the plastic frame and now it sits perfectly even though the aluminium fins touch the passive north bridge cooler - something that i don't like much since the northbridge averages at 60C.
I got me a new northbridge cooler though that should solve the problem once and for all.
Works perfectly fine on my P5Q Pro. No mods needed.
I have the P5Q Pro also, I just swaped out the AC7 for my Xiggy S1283 today, both fit perfectly with room to spare, and I even have Thermalright heatsinks on the 2 mosfet zones and the Thermalright HR05 -IFX/SLi on the NB. That large block on the NB and the tall straight heatsink on the top mosfets are the reason I did not get the Deluxe, the Thermalright one I have up there is about as tall if not taller, but it slants towards the top of the board to allow large coolers
Anyways none of this helps you of couse and its probably too late to switch boards.