Concept SFF layout with standard size component

[staircase]

I just got a full size PSU (Seasonic Prime 750) a few months ago because my old PSU died. Then I realize not that many itx case can accept the new one.

My mobo is also dying (most of the USB port are dead) and GPU is GTX 670, but still usable.

The reason of this custom case is for me to transition to SFF without spending a fortune on everything new. The rough diagram is currently at 15L, and going to refine it and see how it goes.

Green: Graphic card 300mm
Red: Standard size PSU, 150mm x 170mm
Blue: AIO 120mm watercool
Gray: Mobo
Void space: A bunch of existing HDD and SSD (not ready to upgrade to M2 ssd yet, but soon)

My question of the layout is the orientation.
Radiator, GPU, and PSU should vent out, but which orientation would be best.

 

[chx]

The last one: PSU fan intakes fresh air from the bottom and exhausts it to the back. Video card, I do not know whether blower or not but anyways it intakes from the side and exhausts mostly to the back as well. Meanwhile the radiator happily exhausts to the other side , even happier if you put a nice intake fan on the face closest to us. Possibly even rotate it 90 degrees so it's parallel to the mobo and exhausts to the top.

Yeah, the mobo is upside down but that doesn't matter.

 

[chx]

I am not editing that because this is a separate matter: if you were using something like the Silverstone Tundra TD03-E with its 33.5mm high CPU block then you would have a pretty decent case concept at hand -- 170mm (mobo) + 120mm (radiator) is 290mm but you wanted 300mm so that's OK, it's only 170mm + 20.32 = 191mm wide and about 140mm (55mm mobo+84ATX PSU) high which happens to be needed for video card height anyways. Less than 9L but these numbers are theoretical, in reality it might be 10-12L.

Bonus 3.5" disk (or two 2.5" disks) under the radiator on the case floor.

Only problem is any heat the mobo produces is going to be trapped against the mobo. You might need to widen the case to the left and add like two 40mm fans there, even slow moving they will move in some fresh air and that's that. (Gelid Silent 4)