If funds are tight. Competition Products has very good prices on the RHS Vortecs or ProTorker Vortecs, they're better than the stock GM Vortecs + cheaper, as they've been upgraded for more lift, thicker Decks & better cooling.
http://www.competitionproducts.com/Cast-Iron-GM-Vortec-Heads/products/1262/
http://www.competitionproducts.com/Cast-Iron-GM-Vortec-Heads/products/1262/