GM Small Block Exhaust Manifold Gasket Set | Sierra 18-0604GM Small Block Exhaust Manifold Gasket Set Sierra 18 0604 Complete exhaust gasket set for a pair of Sierra 18 1997 1 GM small block center rise manifolds. Exhaust manifold gasket set For GM small block 5. 0L 305 and 5. 7L 350 cu. in. marine engines Includes 2 manifold to head gaskets and 2 riser elbow gaskets For use with a pair of Sierra 18 1997 1 exhaust manifolds