GM performance has factory springs good to .570 lift and they are only around $60 shipped for a set of 16. I think they are ls9 or ls6 factory springs... just installed a set in my ls1.

68 Road Runner, 69 Belvedere, 71 Challenger Vert
340 barracuda, 01 Ram CTD, 95 Ram, 04 Ram, 85 Daytona turbo Z
66 GTO, 06 Magnum RT AWD. 07 Ram CTD, 07 Ram