I didn't have any problems putting the heatsinks on different RAM, but I did use Kingston RAM, so that might have something to do with it. I didn't try any other RAM to see if it would fit.

The reason I am only running two sticks now is because I only had two Hyper-X heatsinks available. I had tried modding some regular RAM heatsinks to fit FB-DIMMs in the past, and it failed miserably. Temps would regularly top 100 C. Since I refuse to have a machine that sounds like a turbine, that's when I went to the Hyper-X RAM, until it died. Temps were fine with the Hyper-X, and they're fine using the Hyper-X heatsinks on the Kingston RAM I am using now. If I had two more Hyper-X heatsinks I might run two more sticks as long as the temps stayed reasonable. But without them there is little chance of that.

Anyway once I am done building my SFF PC replacement, if you want the 2x 4GB sticks of Kingston KTA-MP800K2/8G FB-DIMM RAM with Hyper-X heatsinks on them, let me know. The SFF build is taking more time than I had planned, as I am having to shorten just about every cable I put in it.