According to this site, which has already been cited a couple of times in this thread, (http://www.ngw.nl/int/aus/southaus.htm) the coat of arms for South Australia between 1936 and 1984 was:
That site goes on to say as follows:
The arms also used a female figure holding a conucopia and a sheaf of barley, as well as a farmer holding a pair of shears and a fleece of wool as supporters. The crest showed a staff with a banner with the five stars of the Southern Cross and a lion. The motto was 'Faith and Courage.'
You can see that at the top of the Bomford birth certificate, the words "FAITH AND COURAGE" appear across the bottom of the arms, and you can see a man (no doubt, the farmer) on the right and a figure in flowing robes (no doubt, the female) on the left.
So, the coat of arms appears genuine.
I used your large clean image there to look at the folds of the Aus document and from my eye it appears that the letters are layered atop the folds, rather than being part of the fold as in the Orly doc. interesting to say indeed.
Good find...I was trying to figure out the Coat of arms motto....faith and courage. Couldn’t make out the Courage part.