intake manifold

I don't think you'll pick up quite that much, but the stock lower is definitely hurting it. Budget alternative would be to have tmoss port your lower. Pretty good match with your p heads -- he's got some dyno data on some combos like that I believe. Much cheaper than aftermarket manifolds -- his ported lower makes the stock upper/lower HO manifold flow much better - not quite as good as the GT40/Explorer/Cobra intakes, but pretty close, for MUCH less money. PM him with your combo - I'm sure he'll share his thoughts on what you're contemplating.