In the altered timeline of 6.17 My Heart Will Go On, Dean drives a black 67 Ford Mustang with two orange racing stripes. The car also has silver Cobra emblems on the front wheel panel denoting that the vehicle is with an engine designed by Carroll Shelby, likely a GT 500. It has the Kansas license plates "KAZ 2Y5" which were seen on the Impala for all of season 1 and most of season 2, until 2.20 What Is and What Should Never Be.
A 65 Mustang was Kripke's original casting choice for the role of Dean's car.
When I was originally writing the show I wanted to give the guys an American muscle car. My first choice was a '65 Mustang. My neighbor said it has to be a '67 Impala, because you can put a body in the trunk. He says, 'You want a car that, when people stop next to it at the lights, they lock their doors.' Source.