Oparara to Kohaihai?

Hi I'm scoping out summer routes, looking at the tracks north of Karamea township (though not the Heaphy). I'd like to start at Fenian Road, walk along the Oparara Valley Track to Oparara Arch area, and then... wouldn't it be cool to keep walking from Oparara and end up on the beach at the Kohaihai Shelter? Map: http://www.topomap.co.nz/NZTopoMap?v=2&ll=-41.13528,172.168569&z=14 There is a small zig zag track at the Kohaihai end, and some mountain bike tracks on the tops, but I can't tell if crossing this area would be doable with good navigation skills, or if there are threats in that terrain. Would love to hear from anyone who's been up there. (I know the Honeycomb Hill area is restricted)