1966-1967 Corvette Exhaust Manifold Casting Numbers

1966

Left Right Engine
3846559 3747042 300 & 350 Horsepower 327 Engines
3872765 3872778 300 & 350 Horsepower with K19*
3880827 3880828 390 & 425 Horsepower 427 Engines

1967

Left Right Engine
3846559 3747042 300 & 350 Horsepower 327 Engines
3872765 3872778 300 & 350 Horsepower with K19*
3880827 3880828 390, 400, 435 Horsepower & L88 427 Engines

* K19 is Air Injection Reactor.