I have this for the SB...and it's a good fit.
NCIX.com - Buy Enzotech CNB-S1L Forged Copper Low Profile Northbridge Heatsink Square - CNB-S1L In Canada.
But all in all it's the NB temp that could be lowered quite a bit, allowing me to OC more with acceptable temps. The problem is with the SB, along with everything else...lolz. As the cooler for the whole mobo is one piece. Mosfet cooler is 100% compatible by Thermalrights' list, and the SB does fit nicely. It's the NB / NF200 chips that are the tricky part.