The script held in the Crawford Collection in the AFI Research Collection contains the following character notes (excluding regular characters):
'AMBROSE McLAUGHLAN: 70's. A classic Australian bagman. A rather striking figure.
'BOB WILLIAMS: 40's. Big, rough bloke, but not unsympathetic. Bob thinks his son's a baby at sixteen.
'NICK WILLIAMS: 16. Extremely capable aorund the farm, but probably a bit young for his age in other ways. He thinks he's a man at sixteen.
[...]
'SHEARERS: Actuals.
'SHEEP DOG'.