Couple things...........if you have lowering blocks now, you either have the wrong spring, or them mounted wrong. If the car sits too high without blocks, do something else, because blocks are BAD. Two, a stiffer rear segment won't do dick to solve your problem. The bars are welded to the housing. If they rotate and hit, it's because the front segment is letting the housing wind up. The front segment is too flimsy and or bars are not adjusted right. The purpose of a cal-track or similar device is to stiffen the front segment. The rear segment does NOTHING, but hold the car up.

We have a Nova we run that doesn't even have a rear segment. We use the front half of the spring only, with coilovers. I have it so stiff, it's like a mini ladder bar