the Mercruiser 3.7L engine was based on one Ford 460 cylinder head, the block it self was aluminum, while the head was cast iron. It would be nice to use the aluminum head(weight savings, and simular expansion rates of head and block), but its not needed. I've only seen a few that had head gasket issues, the biggest problem the 3.7 had was leaking manifold to riser gaskets
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