I changed out a front spring on my old c4 a few years ago and it was pretty straightforward. Not sure if I understand your question correctly. The rubber pieces are there to keep the spring from rubbing against bare metal, which will eventually destroy the spring. Also on a convertible the factory used additional aluminum shims, which you might have noticed while taking off the old spring, I think they used 3 of them, many people just remove them to lower the front end a little more. I think the factory used 3 shims to raise the car a little more because of the x-brace.
Anyway, the geometry of the front spring looks a little weird when you're installing it, you look at it thinking that no way is it going to look right when it's all tightened up, but once you tighten the crossmember bolts it all falls into place. It's practially idiot-proof, this coming from a certifiable idiot. I have a hunch this is what's bugging you. Be sure to put some lithium grease on the control arms where the rubber ends rest.
