As others said, the stock gasket should be fine. But while you're in there, I'd recommend getting a set of locking header bolts, to keep the bolts from backing out. There are many different kits and styles out there, just choose one that will prevent the bolts from moving. There are few things more annoying than having to tighten your header bolts every couple of months.
At the very least, use some thread locker on the bolts. Leaky headers are no fun. Granted, you may only have to tighten them once or twice after the install, but personally for me, I'd rather get the locking bolts and not have to every worry about it.