Wize, I'm with you on pre-loading the chassis. I just can't picture the "how to" with a heim setup. (limited scope of vision per se ?) a cage will ultimately make the chassis the most rigid, but the "here and now" was to at least tie the front and rear together.
I was too young to catch the wire car when it was new, but have since found Don's car to be a cool project. It's kinda like mom's cross your heart bra 'eh ??

Vert, A triangle is the strongest shape in nature, especially an equalatteral triangle. that applies to a force exerted to one side. but as for torsional strength, I haven't the brain power to figure it out. In your question, did you mean to make the connectors from triangular stock, or to triangulate the frame (ala rollcage) ??