Are the triangulating bars they sell worth the money in a street machine with a mild build? Do they provide any noticable, improved handling characteristics?

 

On the street you probably wouldn't notice it but going through a slalom or road course it should be very noticeable. They are designed to tie the control arm mounting points together resulting in less flexing and sway in the whole rear suspension. It also helps frame stability and lessons the chance that you'll tear off that lower control arm mounting point. Although that would take some serious hp/tq but I have seen it happen. Several manufacturers make supports that weld unto that mounting point to strengthen it also.

http://www.tntraceshop.com/1964-1972_A-body_180300.html