The "Arnie" was actually called the "Schwarzenegger". It was one of three concepts that would become the 1994 Mustang. The Terminator could have possibly adopted the name internally from the 1992 concept.
I will try to dig up the concept art and clay model pics if I can.
Edit: Well Bam Ba Lam, all 3 on one site... See how concepts become reality.
Ford Mustang Photo Gallery - 1994 Schwarzenegger concept | Shnack.com
The Schwarzenegger yes, the rest no. I'm sure we'll see many concepts before we get a clear idea of the 2014.