Hey All,
I found the original fan noisy, so I was looking for a way to replace it with a Noctua Fan, I stumbled on a Reddit page where someone made a fan duct for the original fan using laser cut acrylic, he provided the lightburn file, which I modified to adapt and fit 2x 40mm noctua fan, I sent the file to a very friendly eBay seller who’s link will be left at the bottom. I connected the fan to the Gpio pins at the back of the argon eon to utilise the PWM feature but you can do it whichever way you want, if you want to make the fan screws sit flush you can counter sink the scree hole like I have. If you do use the eBay link I provided just send the seller the files I have provided. I have also left below the guide to wiring the PWM fan to work with PWM.
Enjoy 
Downloads
https://drive.google.com/drive/folders/19IPUNc22zqwDkNqYTYVMy7_ESSD7lKwC
Credits
https://www.reddit.com/r/raspberry_pi/comments/132s1vq/argon_eon_air_guide_laser_cut_acrylic/