@sally @freetar 0. You want a quality 4-heatpipe cooler with built-in springs - the AG400 works, but the AK400 is nicer.
1. The A?400 happens to come with 4 #6-32 machine screws.
2. Mark and cut the brackets like so.
3. Result.
4. Drill holes along marking (worst drilling job he ever did, as he took a photo for this one, but it stills works).
5. Expand holes with more drilling or filing until you get something better than this (that bad still works fine).
6. Clean up with grinder and fit to cooler.
7. Installed (as you can see it blocks 1 PCIe slot, but that's the slot for the PCIe sound card and it's disabled if you use PCIe slot 4).

You can also use other coolers, but you'll also need 4 springs, screws that fit (that can also hold the springs) and external metal brackets to cut to size.