Gday incey,
Unfortunately the Goldsborough is definitely National Park if not just under the edge of the WH area.
Its hard with NP to know whats what as the borders aren't perfectly marked.
Basically tho once you go across the last bridge your in the NP. As has been said there is a locked gate on the right just before that bridge which leads to the mentioned cane farmers property.
That property goes down to the edge of Tooheys ck, past that your in NP again all the way up to the back of Butchers Creek on the tablelands above.
If you follow the road into goldsborough day area/ campground theres another locked gate which is the very start of the Goldfields hike that goes up over the range - still NP.
Theres another track which spurs off to the right as you walk from the campground, that crosses the river and heads up the ridge dividing the east mulgrave river from machine ck on the other side.
Once upon a time that was the lower part of a 4x4 track called the Old Cairns Track, it was also probably part of the mule tracks to access the diggings further up the valleys.
Again all part of NP nowadays since they locked the 4x4s and dredgers out of there in the late 80s.
Plenty of facinating history up there still tho
TGW