Chris if you do a search for "chassis torsional testing" you will find pics of the test rigs used. There is also a diagram in the VSB 14 that explains the test procedure and test equipment. I was trying to post a pic of my rig but aghhh.
Anyhow check with your engineer regarding your mods, also when comparing Young's Modulus of Torsion between round and RHS sections the RHS is tested in the longitudinal axis.If you lie it down 90* as in your build it is considerably less. PM if you need any help
