The producers were looking for someone beaten and rough for the role of Max. The night before his audition for the film, Mel Gibson had his face cut in a bar fight.
The car that Max drives (the "last of the V8 interceptors") is a production car, the Ford "XB Falcon Hardtop", sold in Australia from December 1973 until August 1976. The car in the film had a standard 351 cubic inch (5.75 liter) V8 motor.
The stolen interceptor driven by the Nightrider in the opening scenes is another production vehicle; it is a "HQ Holden Monaro", which was sold in Australia in the early 70's with a variety of motors including large capacity V8's. Also, the other police vehicles in the movie were sedan versions of the XB, although one was the previous model "XA". They also had 351 cubic inch motors and are a common car on Australian roads.
I had a 351 '73 Mach 1,much the same car.