Here is a different approach to not only adding a leaf to the front half of a leaf spring to maintain pinion angle, additionally it cured wheel hop according to the owner. This reminds me of the old mopar superstock springs with the spring pack stacked thicker at the front, but in a different configuration. Anyone else do this? I would like to add a leaf under the main leaf, but I have original type tri5 chevy grooved springs
The clamps are probably doing more to control wheel hop than anything else. The springs behave more like one rigid beam when they are clamped together and aren't allowed to slide past each other. This effectively increases both the spring rate, and the internal dampening rate of the spring. Be aware that clamping the leaves together also creates higher localized stress and leads to much quicker fatigue failure of the leaves themselves.
Looks like a home made helper / overload spring. Agree on spring clamps, I "tuned" the leaf springs on a street strip car by adding / removing leaves and moving clamps around - trial and error it launched hard and straight.