The aftermarket nut he'd purchased was high, and playing was stiff. I reckoned the nut would need to come down about .020" (.5mm) The landing surface was tilted a little, and I had visions of the binding delaminating and other horrors. I decided to take material off the bottom of the nut instead.
The nut casting is really quite rough. A couple of passes with the file revealed that the perimeter of the screw holes was a high spot. I took it to my rotary sharpening platter and used a course disc to gradually work my way down until I reached the correct depth. It's not a job to rush, and you have to measure constantly.