Other mistake: Throughout the movie we see the mustang rolling chassis in the garage. This is a rolling chassis of a 1967 Shelby mustang gt 500/350. The main ways to realize this are that the car has the cut outs in the front for the 2 fog lights that the Shelby had and that the back end has a spoiler which is built into the body. However the car they do all the driving with is a base model 1967 mustang fastback. While a new grille would've covered up the fog-light cutout, the regular fastbacks didn't have the built into the body spoiler like the Shelby's did. Removing the built in spoiler and making it as smooth as it was would've taken way too much time and supplies. It also wouldn't have served any benefit. You could argue they were trying to eliminate down-force on the back but the spoiler was only about 2 inches, it wouldn't have helped. The directors did this to avoid wrecking the much more rare Shelby mustang.