Plarail Line 0 Inside Curved Track

Exactly. There's life in the old coot yet. All the detail you need is in the Vio's Collection So Far thread, starting about here.  

And the link Vio posted there, to Plarail current part dimensions inherited from the official use of "Large Curved Rail"

Chrisjo, I love that website! Do you know what software they are using to design those? Is it their proprietary tool or something available to public?