Haven't done it yet but I will within a month. I bought a kit that has intake gaskets, block-off plates and coolant re-routing lines (same as ones on Ebay). This mod is not so much for performance improvements as it is for increasing engine longevity. Specifically, making sure you don't get coolant by-passing the EGR cooler and making it into your cyclinders and the resulting head gasket/head stud failure.
2004 F350, Crewcab, 4X4, 6.0L Diesel, Shortbox, 285/75R16, K&N FIPK, 4" turboback MBRP cat delete S.S. exhaust