Ian,
The attached scan is from a book compiled by Stephen Taubert titled Formation Signs and Vehicle Markings of the Australian Army 1903-1983.
It may answer some of your queries, but note that the vehicle used in the diagram is a Cab 11/12 Blitz, so some of the positioning may be different.
Can I suggest if you haven't already done so, that you do some research on the Australian War Memorial site
http://cas.awm.gov.au/TST2/cst.acct_...orer&bos=Win32
Hunt through the photgraphic database for Chevrolet Van 15cwt - you might come across some useful data.
Regards
Jack