I think I found it

[100IH]

Best practice is to assemble the manifolds to the engine with the rings, with carbon removed from the counterbores. Check how close the manifold comes to the block. Look at the thickness of the old gasket that is settled and crushed. When the manifold has been surfaced,the depth of the bores will have been reduced, increasing the gap that the gasket must seal. might have to cut down the height of the rings so the gasket will crush abd be able to seal.