Gordon,
The Rising Sun I photographed was the Aussie one, as worn by all our soldiers & appeared on a lot of trucks. Whereas the one you have, I think, is a Unit tag.
The Base where you got teh truck part from might give you a clue to the unit stationed there in WWII, and then Google is your friend...
Incidentally, the photo I have added is the modern version, & not the WWII version from the Australian Army (
www.defence.gov.au) website.
Ian