Torque Boxes?

Hi
I was reading a post about a dart build-up and the authour mentioned he welded in torque boxes like the ones used in the 27 body, (convertible) for extra strength. Anyone have a picture or description of what he was referrring to?:read2:
I am guessing that it is a subframe to floor extension that is perpendicular to the existing frame rails? Would heve been able to remove them from a wreck or did he fab them?
Anyone?

pete