the iron block is 3 times more dense than aluminum ,and your right the thin walled 98 blocks are a problem,but I sold over 200 girdles and not one failure yet, as soon as that girdle is bolted to your engine, it restrains your block from twisting, and that will definetlley help you bores keep square, but I would stay away from 98 and 99 blocks, because you can only hone them .004 over, while later blocks can be bored .010. yhea the iron blocks are slightly more rigid than thier aluminum counterparts, but who wants to stick a iron block in thier already heavy ass camaro or trans am, thats another reason to run a girdle, plus aluminum looks so much cooler.