I've got a tubular GT40 upper and lower setup that I'll be putting on my stock 5.0. From a little reading, it sound like I can expect maybe 15hp from the swap alone. Lots of people get the lower intake ported -- but they all seem to be running various aftermarket heads. If I get the gt40 lower ported would it give me any significant gains on the stock heads, or is it not worth the cost unless I'm going to swap the heads?