The head and the manifold must be flat where they meet. If you've been dealing with a chronic leak, I]m going to guess that one or both surfaces need to be planed. Hold a long straight edge like a carpenter's square against the head ports, and try to slip a feeler gauge between the head and the square. There shouldn't be more than a few thousandths gap at any of the ports. A good machinist should be able to set the head up in a cylinder head mill, or even a Bridgeport, and flycut the side of the head smooth along the ports. The alignment studs at the ends of the exhaust manifold can be unscrewed with a pair of vise grips.
The rings are only for intake manifold alignment with the ports- - - -they don't do any sealing to speak of. They might need to be filed or ground down a little to allow a milled manifold to tighten up snug against the gasket, however.
Jerry
