[blue00gt]

Even on a stock motor longtubes and the shorty crossover pipe add a good amount of power (15+hp and lb-ft). Shorties only add a couple of horsepower on a stock motor. The difference between the two would only be more dramatic with a blower. Just because you don't see much of a gain by putting shorties on an otherwise bone stock car doesn't mean that the stock manifolds are not a restriction - it's just that shorties aren't that much better than stock and the stock H-pipe with 6 cats is more of a restriction and will not allow you to see the gains with the headers until it is replaced as well.
Why are longtubes not an option for you? In my opinion given the cost and difficulty of installing headers on these cars they are the only ones worth putting on a mod motor, but then again with a blower I'm sure you would see more hp than stock manifolds even with shorties. The only drawback I have seen with my longtubes is reduced ground clearance (I have 3" under the cats), but then again my car is pretty slammed.