Here is the coat of arms for South Australia in 1958. Clearly it is NOT the crest used on the Bombard COLB.
First off, thats a coin from 1938, not 1958.
I am from Adelaide, the home of the Bomford certificate. Its real. And to prove it, heres an interview with David Bomford on ABC Radio Adelaide - http://www.abc.net.au/pm/content/2008/s2646009.htm
That’s the Australian coat of arms, not the South Australian one.
This has been solved, apparently by more than one person.
The seal on the Bomford certificate includes the symbol for the government of South Australia. It has a lion and a unicorn instead of a kangaroo and a dodo.