Even in the 70's we regarded the name Rough Country to be a very apt description of the ride the springs gave. OK mud springs, not very great otherwise. Too few leaves to save dollars. More leaves for any given lift will almost always equal a smoother ride; up to a point. Superlift is more expensive because they use more leaves. Each leaf bends easier by itself. For example, bend a 1/2" thick plate, now bend a 1/4" thick plate. The downside is thinner leaves are not as strong (see example above) so they will fail sooner especially if they are overflexed often.
All this to say...a soft ride equals more money normally. A ride with longevity equals more dollars...normally. Inexpensive lift 'kits' are normally less expensive than individual springs because they are thick, solid bars of cheap spring steel. Ya gets what ya pays for.
Year ago Trailmaster sold leaf spring lift kits for GM vehicles and it was a pretty expensive kit in comparison to Rough Country, SkyJacker, Tuff Country, Rancho, etc. (expensive was relative back then, maybe $50 more). But it worked so much better than the others did. A 6' kit flexed to full bumpstop without too harsh a ride on the street. I had a 6" on my SWB GMC, that's why I mention it, I rockcrawled with it in Colorado and did a lot of river running, muddin, and hill climbing using it in Missouri for many years. The trips cross country where tough I won't lie, but my BIL had a Rancho kit on his Blazer and he was much more miserable, got stuck more often too because the tires would be airborn in a twist.
This likely doesn't help much. I suggest Superlift or Softride springs. Much more expensive but cheaper than back surgery.