I'm not trying 2 b a smart@$$, but I really do not know how anyone can accurately identify these springs w out part # stickers or unusual powdercoat/paint color (based soley on pics of black springs).
This link has a bunch of rate listings for various manufacturers..it MIGHT help... http://www.angelfire.com/my/fastcar/suspension.html
Hopefully someone can tell you based on your cars options (if it came new or from SLP w them).
__________________ Brunton M-spec
1,700 pounds and LS?/T56 drive train... good times! 2012 Colorado
-3LT-ZQ8 Crew Cab w factory 5.3 - pretty stock... T-56 swap? 1973 Buick Century
-delayed by new projects, but swap candidate some day 2002 Hardtop Z28
-MMM M6 Strano-Sway Bars-Springs-Koni S/As-C5 Brakes-Hooker LTs,ORY,CB SOLD