All cast-iron exhaust manifolds in 1963-1965 Corvettes equipped with a small block V-8 engine use exhaust manifolds with a 2 1/2 inch diameter outlet except those equipped with the base engine and the 300 horsepower engines equipped with an automatic transmission - they have a 2-inch diameter outlet.
On this Motor
Left Side - 3846559 - engines with or without AC
Right Side - 3733978 - 1957 Corvette
# Right Side Should Be - 3747038 or 3750556 - Not on engine when purchased