"For starters they are thin wall tubes and ya can pretty much bend them with your hand."

We need to be careful here, in assuming exactly what loads a brace is supposed to resist, ie is it tension, then size, shape, thickness matters little, main attribute is the cross sectional area of the material in the brace, is the brace is supposed to resist compression, then cross sectional area of the brace and the shape and symmetry of the brace is key, being a tube is the most efficient design wise, same attributes apply to axial torque, with the understanding, the larger the diameter, the stiffer, now it we consider beam bending, then it gets a bit more complicated. so I can't automatically dismiss thin wall tubes without a better disclosure of their original intended design purpose. I use a typical plastic soda straw as a great IMO example of the issues on this topic.

I am still I'm relatively clueless, and will remain so, on the "late B bodies"