Updated: Apr 3, 2018
Got a good amount done today.
Finished the motherboard mounting brackets. Decided to just do the 3/4" steel tubing to match the way the radiators are mounted. It also allows access to the back of the motherboard to remove the waterblock if need be without removing the entire board (thanks for pointing that out to me earlier. That was an oversight on my part).
Now that the motherboard is done I started working on the PSU mount. I decided to put it in the space between the motherboard and the pump/reservoir board (not yet mounted). I raised the PSU roughly 1.75" off the bottom of the I beam to allow the coolant lines to run underneath to the pumps and also allow enough room to have the cables plugged in. I designed the holder to allow me to slide the PSU out once the bracket is welded to the desk. I don't think I'll have any issues with it. I needs 3" of clearance to slide it out. This will be good because it will allow enough room behind the GPUs for power and for the SATA cables to come out from the motherboard. I'll be welding the PSU holder in once I know exactly where/how the GPUs will be mounted.
It's all coming together! Yay!