The factory put studs in the head for the front and back exhaust manifold attaching points. Also, I believe all four of those location (two per head) are into the coolant jacket.
I actually blew one right out of the head one early spring just after getting the car out of storage. The threaded exhaust manifold holes in the end of the heads DO go into the water passage. The wall thickness there is also extremely thin so it's easy for them to get messed up. The threads on mine were gone so I installed stainless Heli-coils and studs with thread sealant then nuts on the outer-most holes only. Worked for me.
Not 100% sure but the outer holes may have used those funny conical washers with the nuts. I was working with headers, not manifolds, so it didn't apply.
