Oh wow! My family also had a scrap metal yard.
We had cranes with magnets which was used to load scrap metal from the trucks of clients from where it was sorted and then loaded unto railway carriages.
As for bodies of cars, or other tin items, the crane with the magnet will load the it into the press from where it would be pressed and then onto a railway cartridge.
I can also remember my dad always walking with a magnet in his pocket testing for steel or aluminium. 😊