I wrote a tech article on torsion bars for Mopar Action a number of years backed and listed some calculations that showed how much stress the /6 bars are under in a car. Using /6 bars in a B body is just asking for trouble since the bars are under so much stress. A small knick or gouge on a /6 bar in a B body car is enough to start a crack. The bigger bars are way less likely to snap since they are under a lot less stress. Bars bigger than the factory Hemi bars probably never snap unless get damaged really bad.