How much chassis stiffening needed?

A56 said
Not quite sure what you mean by factory cars, but my 340 cuda has all four of them (torque boxes). Agree that torque boxes and "heavy" torsion bars (1.03 or bigger) as well.

not trying to be too technical here, by "factory car" I just meant some cars that came "stock"/ "off the line" / "off the lot" / "factory equipped" with torque boxes, from convertibles to small blocks to hemis, or even my car that came with none of the above. None of these cars ever came with frame connectors