It's ironic to find this thread at this time- I restored/modified my charger in the 80s and also liked the look of ladder bars. So, I installed a pair of used ones off my buddies car, which I think was a Chevelle. I beleive most of the older style ladder bars were made for coil spring cars, but I bolted them on anyway.
Well, 20 some years later, I am digging my car out of storage, and trying to figure a way to keep them on the car, realizing they are not needed. I think mine were made by Lakewood back in the day, and they just clamp around the axle housing. I now realize that this can cause the rear suspension to bind, although I dont recall having any trouble while I drove the car back then. But knowing better now, I am thinking of making up a floating axle clamp of some sort to allow the axle to rotate as it wants too. I am also pulling the springs out of the car and will either have them rebuilt/rearched, or replace with superstock springs.