See other posts here. Everyone uses different springs & some have had trouble with theirs. I bought GM SS springs from the Dealership. I don't remember the price but I work there so it would have been less.
The way I figure it, the GM springs would be the best bet only because Chevrolet has it figured out for the SS & has to warrantee them. The SS springs are about 2-3 inches shorter & lowered my Caprice about 2.5 inches. If you already have a SS & liked it, you better keep the factory stuff on there. My parts man friend put Ibocs on his car & it would bottom out. And it didn't set much lower than mine. They were progresive rate springs. He also put 20's on it. Looked like hugh flowers. Took off some 17 inch Boyds. Looks terrible now. You out there AL??