Plenty of branches and time to catch one if ya did fall or breakout.
I'd say, and be guessing.
I'd use dynamic rope and a series of anchors on the trunk section similar to rock climbing for the last 30' say.
As you go up whack another girth hitched tape in with a biner and clip in the dynamic lifeline which is being belayed by the other bloke further down, was 2 of them.
If something busted and you fell you'd get knocked up but live! Still have 2 lanyard, you could see the branches close enough to walk it, no air humping.
I asked Tom Greenwood how thin and what it was like when he measured that Tassie regnans. He said you have to get right up there on that skinny stuff and physically put the tape measure to the tip ... eeeeerrrrriiiiieeee maaaan.