By the late 70s/early 80s there was very little freight on the Murwillumbah branch line. There was a regular fly ash train that took flyash from Murwillumbah down I think to the cement works near Wyee south of Newcastle. Also some sugar carried southwards as well. And I think that was about it. By the late 70s most of the perishable traffic (bananas etc) had gone over to road transport.
As far as the sleepers on the overnight train (which had several names during its existence) they would have normally been FAMs as these were specifically built for this train. But I'm sure there would have been occasions when Aurora sleepers would have made there way into the consist.
Hope this helps.
Sorry - meant to add a note about the locos. Would have normally been any loco that operated the NCR at this time. Mostly 442s and 48s with maybe the occasional 45.