Thanks for having taken the time to re-write your question.
Actually, my wishbones were not made with flat-oval section tubes, but with round tubes as per the book (they come from Talonmotorsport)
The pictures I published above are the wishbones for Locost sold by Rally Design (not suitable for Haynes Roadster), to show Jason that they were not made of square section tube, but of flat-oval section tubes.
I have no idea what are the dimensions of the tube they use.
If I had to made a new set of wishbones for me, with flat-oval section tube, I will try to find what is the strength equivalence of the round tube used for the book wishbones in flat-oval section tube, like in a simulator such as you can find on internet.
Hope that answer your question