they also make the car look lower.

They were part of the exterior trim package and are very rare. My 68 L79 had them. I have also seen them on 4drs and 2drs. That's what makes me think they were part of the exterior trim package. Another one of those 68 only parts!

My 68" Nova has the original set on it . They are in perfect condition and most likely I will put them in storage when car is done as I dont like how they look anyhow

I think the key thing with the rocker curtains is that they were discontinued and/or were installed inconsistently. We've seen cars with exterior decor with & without, early and late - bothersome!!