Very interesting stuff here. Very similar to our study. Here is my two cents worth on the topic.
I have been studying a bit of data covering the structural analisys of a NASCAR chassis.
A lot of it applies to unibody construction.
For example. The major chassis members are...
The rockers and central cross brace (on a unibody the rockers and the seat pan that runs from rocker to rocker) are the major lower structural members.
They tie from the rockers to the frame rails with structural tube. (Torque boxes on a unibody)
Then they have the frame rails front and back with a cross brace at the front and rear
suspension mounting points. That is it for the chassis.
The major torsional members in order of sensitivity to torsional loads translated from NASCAR to unibody are
1 the roof structure that runs from the "A" pillars at the windshield to the "B" pillars behind the drivers door.
2 The strut towers and any reinforcement that runs from the tower to the firewall at the "A" pillar.
3 The "A" pillars themselves.
4 The front frame rails from the firewall to the core support.
5 The rockers and the torque box structure.
6 The structure at the top of the windshield.
7 the structure at the botom of the windshield or cowl area.
8 the frame rail extension that runs from the firewall to the seat pan structure.
Addressing these 8 areas is where the best bang for your buck will be in reducing torsional deflection.
I find it interesting that, under torsional loads, the area under the greatest stress is the roof structure at the edge of the roof just over the side windows.
Of course if the "A" pillars and other areas of the car are not correctly reinforced none of the loads will transfer to the roof, etc, etc, etc...
We have just about finished all of our modifications (sans roll cage) and we have reduced torsional deflection (applying 750 lbs to the front
suspension mounting point) from 1.33" to just over 1/8".
Bob