here to Sell Your Mustang
Ford Mustang was introduced as a 1965 model that was based on the compact Falcon to lower production costs. It came with an obligatory back seat and a multitude of options that would give the buyer an opportunity to customize their purchase, and generate extra profits for Ford. Plymouth faithful stress that their Baracuda beat the Ford Mustang to market by two weeks. But it was the Mustang, which racked up over 22,000 sales its first day and one million sales in its first two years, that turned the market and people’s attention to the pony car. The pony car class that the Ford Mustang helped create is the only class of muscle car that still exists today.
The 64 1/2 was a true 1965 model year car, but collectors use "64 1/2" to help differentiate it from the full production 1965 models since so many little things changed that first half year.
1964 Mustang For Sale - Classic Mustang Trader
The original 1964 1/2 was only available as a coupe or convertible body style. The now famous fastback was introduced in 1965, the first full year production for the Mustang.