Vortec heads, the ultimate bolt on. Guaranteed 20-40 hp over any previous production head design, including fuelies. You can get an assembled pair from GM for $550 and the only other parts you'll need are rockers, manifold, and valve covers. Vortec heads on a stock short block with a little extra cam is good for 350+ hp. A stock 73 350 made 260ish crankshaft hp.