I did toss that up but as you can see the GPUs take up roughly 190*170*360mm of space each. I might make a quick mock up of them though in a orientation with a horizontal mobo.
Make a more cube like case estimate dimensions of 400mm cubed would have 4*180 fans on the front and 2/3 on the rear depending on how GPU and mobo sit.
I am looking to go out the bottom or the other thought is go slightly wider so that io slot fits beside the fans.
Wider might be the go as it'll give me the extra clearance if I modify the GPU cooling and will give me space on the front of the case too for power/reset and USB ports.
Also still deciding if I put DVD/Blu ray drives in this PC because it's been about 5 years since I used one on my main rig. The HTPC and laptop use DVDs still but not this.