Use any good desktop AMD socket 754/939/AM2/AM2+/AM3/AM3+ heatsink if you want a quiet heatsink for C32. They are the same size but don't use bolts like the standard C32 heasinks do, they use a cam-lock clamp. You will need to use a heatsink mounting bracket to use these clamp-on heatsinks. Some C32 boards include them in the package, but TYAN does not include them. Get yourself a Socket 754, 939, or 940 heatsink mounting bracket for a few bucks from eBay and screw it down to your board's backplates and then install a normal AMD desktop heatsink. Sockets 754, 939, 940, C32, and most Socket F units have the exact same screw hole pattern (two holes 3.5" apart) for attaching a bolt-through heatsink or heatsink mounting bracket. AM2/AM2+/AM3/AM3+ use identical heatsinks as 754/939/940 but use a slightly different bracket with four holes (but also 3.5" apart end-to-end) rather than the two holes for 754/939/940/F/C32.
If you want a specific recommendation for a heatsink I would recommend something like the Cooler Master Hyper212, Xigmatek HDT-S1283/S1284 or any other 120 mm tower type AMD desktop heatsink. Your case is large enough to fit those easily. Opteron 4184s are not particularly hot-running CPUs and you will can run very low-speed fans on a 120 mm tower heatsink to cool them quietly. Server heatsinks generally do suck, with the exception of the VERY expensive Noctua NH12DO-A3 and NH9DO-A3. Those Noctuas are "proper" Socket C32 heatsinks that bolt to the board but they cost $60-80 apiece and don't work any better than the $25-35 units listed above. Nobody who knows what they are doing uses a Noctua on a Socket C32 board.