I'm in the process of fitting a 120mm x 120mm x 20mm fan under my Nexus heatsink. I'll have to sacrifice one of my ram slots, and had to make other modifications to the CPU VRM heatsink (cut it smaller). I have to cut one more corner off my fan so it doesn't interfere with the ram slot. Here's some pictures I've taken throughout the process. I originally wanted to use my gentle typhoon fan, and it would fit (after cutting corners off), but the bends of the heatpipes prevents it from sitting under the heatsink fully. I might take another attempt at fitting the gentle typhoon fan later on. Just want to get the 20mm thick fan working at least to see if there are any issues.
https://goo.gl/photos/RkQLiX9XxbLHA3NMA
The fan is a DEEPCOOL Gamer Storm GS 120 PWM Fan Hydro Bearing 120X120X20mm
https://goo.gl/photos/RkQLiX9XxbLHA3NMA
The fan is a DEEPCOOL Gamer Storm GS 120 PWM Fan Hydro Bearing 120X120X20mm