Eleven N class were built, numbered 1871 to 1881.
These had combined air compressors and vacuum exhausters (since WAGR narrow gauge used vacuum brakes except on heavy haul operations.) These compressors overheated, and they were removed from 1871 to 1874 and replaced by simple air compressors. It must have worked because these units lasted quite well.
I'm not sure about Austrac buying 1874. It never left WA, largely because it was still narrow gauge. They might have bought it for spares, but it was complete and used by South Spur in WA.
NA 1872 and 1873 were overhauled and returned to service as NA class before being converted to NB. They were used on transfer work between Forrestfield and Kwinana.
1872 and 1873 used bogies from BHP M636s sold to Goninan.
1874 used bogies from Hamersley units sold to Engenco.