No AIO, just AIR COOLER HEATSINK...First did you mean AIO? And if so there is none. Best you can do is a 120mm AIO/slim fan bottom mounted under the PSU with a medium tophat. But there is no way to use one without a tophat.
Air Cooling Test Report (on page 1) doesn't show Alpenföhn Black Ridge or NoctuaNH-L12 S (modded?)...
...so, is still NoctuaNH-L12 (bottom fan only) the best choice?
(of course undervolt & underclock in this situation should help)