Narrow Backed seats
In the parts image, the seats are the standard narrow back type, not the Australian wide back type which entered production in early 1944. So IF these are the original seats, the truck is not a 1945 period vehicle produced in Australia by GMH.
Robert's images of the chassis numbers are your best guide, along with Keith's comments. If you cannot find the remains of something like that, then the suggestion that the number stamped into the chassis is a later, police/registration dept requirement because a chassis number could not be found becomes the most likely scenario.
Mike
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