Well I can tell you that a bar that has had a hard life,can be used up.
I had 6cyl bars and drilled shocks, worked good untill we mad the trip down to VMP about 400 miles down 301 with them expansion strips. The car bounce all the way down on the trailer and the bars were like wet nondles lost all there stored energy. I guess I should have put some real shocks on for towing. I would get some new bars not junkyard bars.