Ate you talking about the 4.8l V8 or the 4.3l V6? If you are planning on the V8 I would imagine you won't need the V8 springs. Most swaps I have seen with original iron head / iron block 4 cylinders ended up either staying the same weight or even losing weight. I have a shop in Americus (about an hour south of Macon) and we do LS swaps. I'll shoot you a PM with my contact info. I would be glad to help answer any questions you have.
2012 Sierra Denali 2500HD
2011 Harley Road King Classic
2008 Harley V-ROD VRSCDX Night Rod Special
1997 Nissan 240SX L92 / T56 (Stolen and burned)
1966 Datsun Roadster 2.0L Ecotec LNF Turbo (new project)
1965 Chevelle Malibu SS