aftermarket heads???

Don't concentrate too much on just over all flow figures alone when looking at Modular heads. Truth be told, 95% of the 4.6’s out there aren’t enough engine to even justify anything more than ported stockers anyway. A 4.6L engine doesn't require a head that supports that much volume, since it’s displacement is considerably smaller than either the Ford 5.0L or GM 5.7L engine. Yes, if you’re building an all out, stroker complete with cams and a hard hitting level of forced induction then yes, you might find yourself maxing out the stock casting, but otherwise, you’ll never see it, nor will you have the need for a higher flowing head. Just because you purchase a head that will flow a larger volume of air, doesn't mean you'll ever see that level of flow, or use it to it's full potential. If that were the case, then it wouldn't make sense for the 5.0L guys to run anything less than AFR 225's on their mild bolt on cars. Volumetric Efficiency is what you should be looking at, not just overall flow figures.