No. Product life cycles in the auto industry in the 1960s averaged 7-10 years. A new car took 5+ years to design and bring to market. Today, it takes 3 years to bring a new car design to market.
Youre quite wrong. The original Mustang lasted from 64 1/2 to 68, with the 67-68 models being a fairly major revsion in themselves. The Chevelle had a 64-67 product cycle, the Corvette Stingray only lasted 4 years, the Original Camaro/Firebird only lasted for 3 model years.