Yep. Landrum Launchers. They are snappier than any SS spring I've ever had. Only about 4 Lbs heavier for each as well.

Not for nothing, but a real street driven Duster in our club with a full interior, stereo, real pump gas drinking small block with iron RHS heads, all steel except the front bumper and double hump factory scoop scoots to the tune of high 10's on raggedy Mex-tec SS springs.
I would guess that the latest Cal-trac system is simply a stiffening ladder bar from the center line to the spring eye along with tuning thrown in. Perhaps, that is the point that the SS made back then, but with much better resistant steel material.