looks like jegs and ford racing has solved the problems with using the gt40-p heads, they have some high flow shorty headers. page 191 z of the jegs catalog, part#397 m 9430 p50.
there is also a really cool 4.6 liter "carbed" intake, and an electrics kit on page 186 z.
just a little info for active imaginations. i'd like to know more about the 4.6 manifold and how the electric kit fires the ignition......seems interesting.