Based on your diagram above, it looks like you were planning on using it in the standard layout, so no GPU riser would be needed. That's the way I built. GPU just pops into the motherboard slot like normal. Works great.abandoning my M2 build, no GPU riser or side window in stock for 6 months now, need to get building.
anyone interested in purchasing a Black Crater M2 (an in UK), PM me
all still in original box, extra rad/fan mount, front case fan mount and feet (3D printed)
Were you hoping to use the riser cable with the window then have rads top and bottom rather than side and bottom? I thought about doing that (sans window and riser cable) but the odds of everything fitting seemed worse.