Exhaust manifolds, for sure. Marine engines use exhausts with built in water jackets. On twin engine boats, one engine usually runs backwards, like the Allison V12s on a P-38 fighter plane. The torque reaction on the props cancel each other out to prevent the boat from trying to run in circles. Reverse rotation engines have an oddball gear drive for the camshaft, and a rear oil seal that must be swapped out. Most marine engines will have a lot more "full throttle" hours than street engines, so they're usually built with racing engine bearing and piston clearances- - - -a little looser than a land-based engine.
Jerry
