I've been surfing other Blogspots recently and came across Barcoola. http://barcoola.blogspot.com/
Barcoola has always been a favourite HO scale layout of mine - capturing the inovation of the AN railways.
A few blogs refer to the PN steel wagons that run to Darwin on the Freightlink service. They are referred to as RKWF wagons, however, only 3 are allowed to run to Darwin. As such, these three are coded RKDY and not the standard RKWF/RKWY.
The reason for the different code (and restriction on other wagons running to Darwin) all has to do with the wheel profile. The standard profile that PN run across Australia (WPR2000) is not allowed on Freightlink track, and as such these 3 RKDY wagons are (or at least were) the only three PN wagons running around with the ANZR wheel profile, and were limited to Whyalla/Adelaide to Darwin only.
These wagons also have some pretty unique stencils on the sides.
To the Barcoola boys - if you ever need any reference or details photos posted, just ask.