Your situation is similar to my own, as I am also building a dual Opteron workstation with a Parhelia. I ended up building my own case for it, more for the entertainment than anything else. If you're curious, you can see the case build here, which has some intersting stuff in it:
http://www.modthebox.com/cgi-bin/yab...num=1076781082
But to the liquid cooling of Opterons, the only decent solution I've found so far is by PolarFLO, but I think their solution is rather cheesy, just a pair of brackets hung on their existing blocks.
D-Tek is in the process of making new top plates to accomodate the Opterons, so that may be worth waiting for.
As to cooling the Parhelia, any "universal" GPU block can work if you're careful with the mounting holes... measure twice.
My experience with it however, leads me to let it remain air cooled, it just doesn't need to be liquid cooled and isn't loud enough to get any noise advantage with liquid cooling.