From a Metal Worker/Welders' point of view what Backyard Tony is saying is not entirely wrong. I'm not defending this guy, He has some funny ideas and most of them I question, but, I am willing to listen to Him. If a current Chrysler Engineer or Metalurgist could counter this subject I would really like to hear it.
As I see it, the 4 torque boxes installed at the factory would have taken more time and cost more to install than a simple one-piece frame connector. Period. None of you have commented on how thick the rocker metal is or the fact that it actually is a frame for the car? A T-boned Chrysler Product shows how much strength/metal is in this area. Obviously Chrysler knew what they were doing plus, they were years ahead on Unibody construction than anyone else. I've taken a long hard look at my E-Bodies' torque boxes and I can still slightly justify putting frame connectors that weld to the floor pans and rails, but I will be making my own because I see a flaw in the currently offered design. I want a super-rigid car and know how to get it.
The old rectangular tubing stuff that was bolted or welded in, I would not wast my time with.
At any rate, look under a new Mustang or Challenger to see what they do their Unibodies. Look at the '70 TransAm T/A, AAR race series cars? Works for them obviously.