On my cousins car that was how GM changed the spring rate...by adding leafs. I'm not sure how Chrysler did it. The trick is finding the OE spring rate and then getting ESPO to tell you their spring rate. Unless ESPO make it public.
Mopar did add leaves, not sure about the strap thickness, the ESPO 2" drop 6 leaf I have the strap used is ~.020-.025" thicker than the stockers.................