You can trim the GC's original heatsink using ashen's technique to the height of the onboard caps, then some space inside it for a fan. IMO this is the best heatsink technique for the GC, Tchay and Zenloc have lots of experience with this, they might have some slightly better alternatives, but I dunno. If you can have fins, get fins. You will always need a fan though, according to Tchay(I think?)
SS