So
Destraex, i may have to publish a retraction, lol
Turns out there is conflicting info on these L2a1's variants with the 'trumpet' recoil reducer, they were produced @ lithgow as part of contracts for the newly formed Malaysia & for the singapore police.
Many sources seem to be confusing the fact that, while these were indeed made in Australia, thats not necessarily the style that the Australian Army adopted.
i'm not conclusively saying there were no 'Trumpet' L2a1's in Australian service, (because well sometimes there are anomalies), but seems far and away more likely that the one with the SLR Birdcage & tangent sight, was probably the only one adopted for use by Australia's & New Zealand's Armies.
You are right, the developer's may need to change their model.
further reading on this, try Ian skennertons L1, C1 book or The 3 volume "collector grade" book of the FAL