Scroll down page for photo guide on installing Mnpctech NCASe M1 Vertical Mount, https://mnpctech.com/pci-e-riser-cable/mnpctech-ncase-m1-vertical-video-card-gpu-mounting-bracket-black.html
It should still work fine with the V6 design update
I can see how orientation is ideal for the ncase panel vents, but agree about cutting the rear opening, there is also small version that can be used in scratch builds, https://mnpctech.com/vertical-gpu-video-card-installation-mount/
Not for everyone's aesthetic tastes, but great for maintenance and buying internal space, consider EK DDC Pump/Res combo with EK Uni pump holder mounted on back of the chassis. more details / photos here, https://0x7d.com/2015/ncase-m1-workstation-computer/