The N was required due to new requirements for all trains to be fitted with ICE radio (Steamrail at the time were yet to fit any of their Steamers with ICE radio, they have sinced organised a portable set up to carry on their trains, alleviating the need for modifications to all of their heritage steam locomotives)
I can clearly remember standing on the platform at Maryborough, looking into through the cab windows of A² 986 and seeing an electronic control panel fitted to the underside of the cab roof, above the driver's seat. This contraption was not present during the 2016 Steamrail open day.
The device in question looked the same as the one installed in the cab of T357 shown in this SRHC blog post about fitting ICE radio to their T:http://srhcblog.blogspot.com.au/2017/09/late-september.html
(21st photo down the page)
This would suggest that the A² already had it's radio fitted at the time of the Wycheproof trip.
I can also remember being told at the 2016 open day that there was no portable ICE radio (this was from one of Steamrail's people, and I don't know if this has changed since)
Also, doesn't the leading loco have to be fitted? As the A² lead the train on the return trip (and was the only loco on the transfer to Maryborough) it would presumably have to have ICE radio fitted...