No mods. I used both plastic washers on top between the mobo and standoffs, small one first, then the larger diameter one. That gave enough clearance. Other than that, it is a tight squeeze getting the standoffs through the holes, but they do go through with some effort. It also makes it tough to screw the standoffs into the plate under the mobo. It would be easy to strain a little, slip, and do some damage. I read that Thermalright had different standoffs for the nf7-s, but I don't really know if that is true or where one would get those. With a little fiddling, it worked for me out the box.
One other note. When the slk-800u mounting plate is mounted, the cpu socket lever is blocked from going up/down because it can't go out a little to clear the little latch. I did find that I could sort of bend out the lever at the middle with a small flathead screwdriver and get it up/down.
I really like how stable and stationary the 800u is compared to the 800a. 800a can slide around a bit and can be accidentally mounted with the base up on the little ledge of the cpu socket. I don't think that could happen with the 800u.