Somewhat hijacking of the thread, but while it was a red hot political debate in Australia during the period, the actual numbers of troops over time were small in comparison to the US and ARVN, even on a population proportional basis-South Korea had several times as many men deployed there, a fact largely forgotten these days. Australia has only had substantial armed forces during the 2 World Wars-sending anything more than a brigade overseas has been/is beyond our capacities.
As to the SLR and bayonet, they were issued it but dragging it along through the scrub fixed was not a good idea on what was already a long and heavy weapon in close country-I doubt they ever left the scabbard except as can openers!
Edit PS-the P56 web frog for field use and modified blackened P37 frog for parade use along with the long and short point bayos.
However, it is a pretty offensive thing to say without explainig what you mean. I am not Australian but I am a former British soldier and I reckon my digger colleagues (I served with quite a few on exchange visits to us) would see it that way. Also it has no bearing on the subject of this thread.
Anyway, as for the question. I can think of no reason why the bayonet which is part of the CES (complete equipment schedule) of the rifle, would not be carried in the field. In the case of British '58 pattern webbing there was a frog built into the side of the left hand magazine pouch which tended to make the bayonet hard to see. I think the explanation might be similar in the Australian case. Aside from parades or certain guard duties the bayonet is very unlikely to be seen mounted on the rifle except in an action where it is about to be used to assault the enemy.
As has been said above there is clear visual difference between the British and Australian versions, particularly the shape of the fuller end. I also have never seen an Australian bayonet with any markings at all whereas the British one bore the partial NATO Stock Number and a partial nomenclature L1A3 and a letter and number for the year of manufacture eg D70 on the grip. Some had a broad arrow on the pommel some did not. The tip of the blade is a different profile I think if you compare them side by side the British one being lorger and more "bowie" like. All the Australian ones I have seen have been fully oxidised, a dark grey with a slight green tinge to it. The British ones were generally painted an eggshell black on the grip and scabbard with the blade being parkerised (from memory going back some thirty odd years). The one shown is definately Australian and in mint condition by the look of it.
"War is an ugly thing, but not the ugliest of things. A man who has nothing for which he is willing to fight, nothing he cares more about than his own personal safety, is a miserable creature with no chance of being free unless made and kept so by the exertions of better men than himself."
I stand corrected on my comment that Aussie bayo' never carried markings......a superb example posted by the OP