Anyway, I eventually gave up looking and did my own 'old school' drawing, so I could make a template for my 'corners'. A good starting point.
I went with 60mm between centres, a whole number, as against the 58.??mm I've seen on some drawings. To me, this dimension isn't as critical, it's ensuring each piece is identical to the next that matters more. I didn't bother with all that chamfering either.
A template was marked out and cut from MDF.
Copies were marked and roughly cut out with a jig-saw.
Six vertices are bolted on two threaded bar off-cuts, the perpendicular holes marked as per the drawing, and drilled through.
Here is one Vertex test fitted.