Modified the initial design to reduce the depth for 14-15mm fan on my Neptune Max 4. It's probably still too tall to use without printer feet mods. I'm using a Thermalright 92x15mm FDB fan with mine, but a Noctua should work as well. I removed the printed fan shield in favor of using 92mm wire shields. 

Buck conv amazon link:  HiLetgo 2pcs LM2596 Adjustable DC-DC Step Down- https://www.amazon.com/HiLetgo-Step-down-Converter-1-25-37V-Voltmeter/dp/B00LSEBYHU?ref_=ast_sto_dp