It's a plain-vanilla IBM Intellistation 6850 workstation, save for the fact I stuffed two each Xeon MP 3.0Ghz hyperthreaded processors in the sockets, which is something never intended for either these machines or the i860 chipset.
They generate too much heat for the stock stainless steel/copper heatsinks and wind tunnel shroud, but I really like the performance of 4 Xeons running together. SpeedFan and the BIOS reported CPU temperatures in excess of 60 degrees Celsius, so I had to do something. I ended up purchasing a Koolance Exos 2 and a pair of CPU-300-V10 waterblocks, as well as the Socket 603 adapters and a drain valve assembly.
I'm water-cooling just the processors for now. The Radeon X850XT video card and Northbridge may get waterblocks eventually, but they weren't the cause of the real heat problem in the big black IBM case.
Running a leak test for 12 hours prior to firing up the system:

No leaks, firing up the system and running 4 examples of Toast to max out the processors:

12 hours later, at the culmination of the stress test, these were my CPU temps:

System chugging (gurgling?) along, 3rd temperature probe showing Northbridge temp of 41 degrees Celsius:

It's hit the mid 90's Fahrenheit here in June, and the house air conditioning is holding the indoor temp at 79 degrees Fahrenheit. The Koolance is keeping the computer at 36-37 degrees Celsius, albeit with the fans set at Level 7. They're still barely audible, and the whole rig is considerably quieter and cooler than when it ran straight air-cooled. I had trepidations about the effectiveness of an external water-cooling kit being used in such a hot-running system, but no longer!