These manifolds are cast from high quality molds for proper fit and appearance. Includes exhaust flange bolts, nuts and washers. 1964 - 1967 6 cylinder owners wishing to improve performance can run a 1968 - 1973 exhaust manifold which has a larger port and more free flowing design. This in conjunction with a larger diameter exhaust pipe and muffler, is the same principle as adding dual exhaust to a V8. Better acceleration, more power and improved fuel efficiency.