Metal Intake Manifold Gasket

The metal ones are usually quite a bit thinner so port alignment can be affected. Sometimes that's a good thing, sometimes it's not. You can tell which will work the best by setting each in place and setting the intake on and see how well the bolt holes line up. Metal ones also require sealer. A shellac type works best IMO... I believe the reason Sir Dan found the metal ones only work on 318's is because their for the small port heads. They have a sealing ridge that'd probably fall into the larger 340/360 ports.