318 gasket recommendations

The air ports can be tapped and plugged with set screws. The factory rarely used an exhaust manifold gasket. Most of the time it was just metal to metal. Both surfaces are machined so you shouldn't need one. I'm not running gaskets at all on mine and I have no leaks at the heads. If your manifolds are warped then they won't seal. I'd take them off and have them machined. That way you know they are straight. Then, you shouldn't have to use a gasket...but you can if you want to. Have the machine shop make sure they aren't cracked before going to the expense of machining them.