For Leo's and Willie's fight, the actors agreed to actually fight each other. Although they wore knee and elbow pads, everything on screen is actually Joaquin Phoenix and Mark Wahlberg beating each other up. There are no stunts and the entire thing was taken in two takes from three different angles. The next day, the actors were black and blue.
When Leo looks in the rear view mirror and sees Willie and Granada taking off their clothes, they are on the driver's side of Granada's car. When he turns around and looks, they are now on the right side of the vehicle.
What are the differences between the Theatrical Version and the Director's Cut?
A
The Director's Cut is about 2 minutes shorter than the Theatrical Version. A detailed comparison between both versions with pictures can be found here.