The 1967 model year Mustang was the first redesign of the original model. Ford's designers began drawing up a larger version even as the original was achieving sales success, and while "Iacocca later complained about the Mustang's growth, he did oversee the redesign for 1967 ." The major mechanical feature was to allow the installation of a big-block V8 engine. The overall size, interior and cargo space were increased. Exterior trim changes included concave taillights, side scoop and chrome side ornamentation, square rear-view mirrors, and usual yearly wheel and gas cap changes.
Source: Wikipedia (original)