My car is a 65 ss with a LS3. I have Heidts front super ride II and four link. It has coil over shocks and seems to ride really stiff. I called Heidts and they recommend 400 front springs and 250 in the rear. I pulled my springs off today and the rear were marked 300 and the front were marked with green and yellow dots. I'm going to call Heidts back tomorrow and see what the recommend I switch to but that I would ask here first. What springs are you running with a similar set up. How is your ride is it stiff or does it ride on the softer side. With my car you can push down on the bumper and get the spring to compress a little but not much and when I drive it you can feel every bump almost like there's no shock at all.