Recently I've built a few large external radiator boxes: This build log is for an external radiator box to house a 560 radiator, ATX PSU, fan controller, and reservoir. Building the frame for these boxes involves the same basic steps: cutting, drilling, tapping and milling out small areas (so that hex nuts can be inserted into a t-slot post assembly).
I love the versatility of t-slot extrusion. Threaded "holes" can be added anywhere along a slot by using set screws to fasten two nuts around a center nut. I used my Avid CNC to cutout the grill pattern in the front sheet. The radiator will be attached to an inner sheet.
It's my understanding that the client just happens to have an extra ATX PSU lying around. That's all.