The author of this Woomera mobile radio history often wrote technical related articles for the Wireless Institute of Australia magazine. The truck pictured is a Commer Q4 ?
http://users.tpg.com.au/ldbutler/MobileRadioatRange.htm
The list of his main articles:
http://users.tpg.com.au/ldbutler/index.htm
In those days the various government departments built their own radios 'in-house' and even trained their own technicians - the Bureau of Meteorology , the Post Master General, the State Electricity Commission, the Dept. of Civil Aviation were a few that operated along those lines. I wonder if it was a efficient system, but that's how it was done back then. You would think it would have been cheaper to go out and buy a high quality ex-military mobile HF radio or a high quality commercial HF mobile radio rather than pay somebody to sit down and design and build a similar radio in your own workshop.