All 12 exhaust manifold holes are wet so you need to either use studs in every hole and bottom them out so coolant won't leak past the threads or use a good thread sealer on any header bolts you use
Most of the new aluminum heads have blind holes for the exhaust bolts, no sealer needed as they do not go into the water jacket in the heads
BTW, there may be one or up to 4 holes in those headers that need bolts instead of studs, seal them rascals up good