What an amusing line of conversation. I had to pull up the 2010 GCR to see if it had changed much since I first met Jesus at Firebird in 1986.
The rule B.1 prohibits monocoque construction. It's really that simple. A tube frame can be stiffened with two stress bearing panels, the floor and a bulkhead. These panels are clearly defined in the rule. The Radon photos show that panels have been affixed to what is clearly a tube frame in a way that clearly is defined in B.1 as not a stress bearing panel. It's a tube frame chassis. A very clever one.
I, myself am pretty impressed at some original thinking. Engineers usually can't do that. Forgive the use of the expression, but some of you guys are Luddites.