You can use 1" WIDE aluminum Angle ("L" bracket) from hardware / home improvement store to attach the mnpctech vertical bracket, perpendicular.
Cut "L" alum angle bracket to width of mnpctech vertical gpu bracket, then drill two mounting holes to attach "L" bracket to vertical mount, then drill...
@MichtoK2, Goo Gone will remove that adhesive residue around your radiator
Good to know, Le Menthe, I see they're making vertical gpu mounts for the M1 here, https://mnpctech.com/pci-e-riser-cable/mnpctech-ncase-m1-vertical-video-card-gpu-mounting-bracket-silver.html
also consider the new Fractal design, Focus G, ATX Midtower, https://www.newegg.com/Product/Product.aspx?Item=N82E16811352069
Front: 2 x 120mm / 140mm (2 x Fractal Design Silent Series LL 120 mm White LED Included)
Top: 2 x 120mm / 140mm
Rear: 1 x 120mm...