There's no hard and fast conversion between the two grading systems, and anyone who tells you there is doesn't know what he/she is talking about. They are DIFFERENT systems that use different criteria altogether to achieve their grades so the lack of consistency between the Sheldon system with Australian adjectival grades is hardly surprising.
To be honest Australian adjectival grades are generally a lot less consistent than those applied to Australian coins by PCGS. Why? Because most dealers in Australia don't disclose WHAT grading system they use, sure they might call a coin VF but according to what standards? The ANDA standard? Their own? English grading? A random grade generator? Grades assigned by the phase of the moon and star signs? In far too many cases your guess is as good as mine.
I've been getting Aussie coins graded by PCGS for several years now and sure I've had some grades that have left me scratching my head and some that I plain don't agree with. But you'd be surprised how many dealers in Australia simply cannot grade at all according to ANY apparent system. I can think of at least 3 major Australian dealers who simply cannot pick (or choose not to disclose) a cleaned coin, two others who simply don't assign grades to their coins because they can't grade, and one who won't assign a coin an UNC grade because he simply cannot make up his mind if a coin is UNC or not. These are MAJOR dealers who advertise in CAB, not
ebay fly by nighters. On the plus side there are dealers here who do a good job, At the Toss of a Coin in Adelaide is a great grader and Klaus Ford is one of the few dealers (love him or hate him) who at least tells you what standard he grades to.