Thanks to everyone...
I found the picture of the RAAF airfield in Tarakan and I agree the dates make a Champ very unlikely, besides, I could only see a tiny thumbnail image.
Here are some interesting pictures of Champs as fire appliances! Including one intended for airport use.
Austin Champ Fire Engines
Ours is an aviation museum not restricted to military matters although some of our best exhibits are ex RAF,RAAF and RNZAF.