Wrong again. The Ford Fairlane in the late 60s had a 3 year product cycle, just the 67-69 model years, the Chevy Impala/Caprice had a 4 year cycle. Also most Chevelles were not muscle cars, but the midsized GM car that people bought to go from point A to point B.
A little reminder of very popular Richard King, WLW Cincinnati, 1960s. One of his sponsors was a Ford dealer and he'd get away with telling his listners to go there for a real good Falcon.