If you can swing the Calvert mono leafs somehow too, that will show you a huge improvement. They are designed to work together. Your car is already surprisingly quick for having a total craptastic rear suspension. I bet it would really be dangerous with the right stuff under there. You'll probably have to clean your pants out.
Craptastic ?? That a technical term? Lol there's soooo many things that need replacing/improvement. You know I'm trying to cut corners so I can pay double in the end! Lol I could just go with ss springs like i think you suggested a long time ago ?