If you are serious about making your chassis stiffer you might start by completing or adding to the existing body and Kmember welds. If you look at the stock body it is hard to believe they don't fall apart with so few spot welds.
Running through some older articles and this is a good one. For a unibody Mopars are pretty good. I've worked on all types of muscle cars. You want fimsy, check out early Mustangs.
