Updated: Apr 3, 2018
Power washed and scrubbed the entire desk today to smooth it out and remove any loose rust. I wanted to keep the general look of the beams so we didn't fully take all the rust off.
Once it was dry I masked off all the mounts for the Mobo, GPUs, PSU, and radiators then hit them with about 4 coats of black paint.
Tomorrow the real fun begins of cutting and soldering all the copper piping for the coolant system. I'll be buying all that tonight. Roughly 60ft worth and around 100 fittings.