In the 2000 release Eleanor was a 1967 Shelby Mustang GT500
in the 1974 release she was a 1974 Mach 1
in the original release, it was a 1971 Fastback that was supposed to be a 1973 Mach 1. The 1974 was the redesign for the "smaller" mustang. It did not even have a V-8 engine, but a wimpy V-6 that made 101 Horsepower.
" Eleanor" Is a 1971 Fastback Ford Mustang played the role of a 1973 Mach 1 Ford Mustang, a true lady both beautiful and tough and is the "Star" of Gone in 60 Seconds. Eleanor is the only Ford Mustang in history to receive Star title credit in a movie…making "Eleanor" a household name.
http://www.gonein60seconds.com/elenor_t.htm
The 1974 Ford Mustang was completely - and I mean completely - revamped from the 1973 car. This car was so new that it was even given a new name: the Mustang II. Not only were the name and look new, but the theory behind the car was completely different. No longer was the Mustang a "muscle car." It still was considered by some to be a sports car, but the engine made more of a whisper than a roar.
The base engine was a 2.3-liter inline 4 cylinder, capable of achieving 88 horsepower. The high-end model remained the Mach I, which had a 101-hp 2.8-liter V6 (the same engine as the Mercury Capri of that year).
http://www.cargurus.com/Cars/Overview-c3687-1974-Mustang.html