what's the diifference between convertible v8 springs and hardtop?

The difference is vert springs have a lower spring rate then coupe/hatchbacks do. This makes for a softer ride, and keeps the body twisting to a minimum. I used Eibach Drag Launch springs that are "not made for verts" but they worked fine. Eibach suggested to not use front spring isolators, because it would make the front sit higher then a coupe. That's what I did and it worked perfect, and I didn't have any squeeks or anything. Good luck, bro.