nice work.
But where you want to positioning the fan. The right place for them is blocked by your power supply.
When you move the power supply to the backplate, you have room for two 80mm or 120mm fans.
Yo also have to mill openings in the left sidewall. If you do this in between the slots of the extrusion, it should be almost invisible.
To get fresh air in the enclosure, you have to make also an opening in the right back of the enclosure (with an fan).
To use an straight flat ribbon cable, it is easier to use right angled headers on the front of the TIL311 board.
Attached some pictures from my enclosure (Vector-PAK VP2) and the SMB with TIL311 board.
Frank