http://www.ls1tech.com/forums/showthread.php?t=17319 <---good starting point
and just keep in mind aluminum heads weigh less then iron
headers & thing gauge aluminum tubing weighs less then manifolds & stock exhaust...short systems weigh less then a stock "type" catback...straight tubing weighs less then a Cat. Air conditioning weighs alot. Some aftermarket suspension components weigh less then the stockers ie lca's, kmembers, aarms. Also aftermarket drag rims weigh less then stockers & bias plys weigh less then radials.