The car started life as a standard 1973 XB GT Ford Falcon Coupe. And for the first few years of its life, this is pretty much how it stayed.
Then in 1976, film makers Byron Kennedy and George Miller began pre-production on Mad Max. They needed a vehicle to feature in the film as the black police 'Interceptor' - a high performance, evil looking car.
Around the same time, Murray Smith was hired on as part of the Mad Max crew. One of his tasks was to put together the Interceptor, and he started by acquiring the XB Falcon mentioned above. Then Murray, along with Peter Arcadipane, Ray Beckerley, and various others, proceeded to modify the car to what was needed for the film. The main modification is obviously the Concorde front end, and the supercharger protruding through the bonnet (which is for looks only). The Concorde front was a fairly new accessory at the time, designed by Peter Arcadipane at Ford Australia as a showpiece, and later becoming available to the general public due to its popularity.
The car also received quite a few other, more minor modifications, to complete the package. There was only ever one black interceptor built for the first Mad Max. That now lives in "Cars of the Stars" in London. Their was a 2nd built for MM2 used for the Stunt sceens and then it was rolled and wrecked. It is still in Broken Hill minus 1 fuel tank, whick some prick nicked...
Hope this helps!!!