I just did this. I agree with the above post, unless you have resurfaced the manifolds and head mating surface, without a gasket you will have a leak. I put a gasket between the right manifold to head, and a gasket between the manifold and the heat shield on the left side. I know this is a 340, but for the record, 440/383's are the worst. The correct way is to resurface both, but that requires much more work. If it's restored oe, no gasket.If you are chasing a leak, better check the heat riser--known issue.