confused torsion bars

/6's high the heavy duty suspension option came with the same torsion bars as the standard sb bars. These bars are .850" in diameter. The heavy duty sb bar is .870" in diameter and the big block bars are .890".

I have the .890 bars in my car fist with the /6 then with the 360. I would say these are the minimum size for a /6 or sb car.