I have spoken to several local builder/racers in the area and they all say the stock LS3 heads and intake are good for 450-500 rwhp, just add cam, springs, pushrods, good bolts or studs and have at it. Far less than 4K. I did the DOD delete, add cam, springs and pushrods, ported exhaust side only(Myself) on heads, head gaskets and head studs for1400 bucks plus 2200 for a complete LKQ L76 pull out with less than 70K miles. 3600 for a complete motor oil pan o intake, all accessories and harness/ecm.
A bone stock LS3, LS2 or L76 would be a beast with boost!