You may have to mod the mounting hardware, for example I had to sand the stand-offs, and the screws which tap-out into the bottom of those stand-offs on a Thermalright SLK-947-U to get the heatsink to fit afetr removing the IHS. I've removed two. one from a 2.4C, and one froma 3.0C, and I have heard using Arctic Silver-III's Silver Epoxy (a very tiny bit) between IHS and core will give you an excellent contact point, great thermal trsnfer (better then any TIM) and will revert to the original height. There's about a 2mm difference in heaight as the photo's attached will exemplify.
