More on the cooler . . .
Just as I was about to order the little (compared to my Scythe) Antec cooler I found, I happened upon something better (I think):
Dynatron is not a sexy name in coolers today; but if you check out their website, you'll notice that a few of their coolers look suspiciously like the OEM coolers you may have seen in some servers or sporting Intel or AMD logos. When I checked it's dimensions against the Antec, it was actually smaller. I seriously doubt it will be as quiet as the Scythe, but this unit also supports PWM. Given the Opteron HE's efficiency, I don't expect it to be spinning at Max too often.
Below are a few photos that give you some idea of the relative size of these things. These pictures also illustrate how close a 2/3 length PCI-e card comes to the side of the cooler. The CPU sockets on the Tyan are slightly offset. A 2/3 length card in the first slot of the S2915 would not fit with the Scythe Mine in place on both CPUs.
I'm going to go for it and bolt down the Dynatrons. If the noise is bearable - then I will hold onto the Scythes for one of those really HOT builds. . .