Not 100% relevant, but this is how it's done on my Pembleton. The stays are made by a guy in Belgium who started off making them for the Lomax but now makes them for any 2CV based kit.
As you can see the diameter of the actual stays is quite small (9mm?) but the important bit is the triangulation (6mm) which stops any flexing and vibration - the killer for wing stays.
Cheers, Robin
wing_stay by
Robin Martin, on Flickr