In 1963, pipes were either 2.0 inches or 2.5 inches. 1963-1965 exhaust manifolds could be either 2.0 or 2.5-inch outlet size.
After 1965 all small block engines had 2.0 manifolds, although the higher horsepower engines continued to have 2.5-inch pipes, which had a smaller 2.0-inch connection to the manifold.
Big block engines had 2.5-inch manifolds and pipes. 1963-1967 mufflers were standard, or the optional N11 off-road mufflers, with one less baffle inside, giving less restriction and a more aggressive sound.
Regardless of the pipe size or engine horsepower, muffler outlets are always 2.0 inches.
The factory offered an optional side exhaust from 1965-1967 with 2-inch or 2.5-inch inlet pipes with aluminum covers—option code N14.