[Technick]

At this point, with the level of mods to the car, and considering the hassel of installing headers, get it over with and install the long tubes. If you have a tubular K-member, so much the better. If not, if you can afford it install a tubular K-member at the same time. I have found that the fastest way to install headers on the 4.6, be they long tubes or shorty's is to drop the K-member out of the way. That means having to support the engine from above, but it makes installing the headers a breeze, especially if you have access to air tools and a side post lift. The major up-side is the fact that you should never have to up-grade the exhaust system again despite any future mods you may do outside a full on purpose built drag car. For the effort required the shorty's just do not provide the bang for the buck, 10-20 H.P. tops. I have installed BBK long tubes on both Cobra and GT 4.6 engines and they have great ground clearance and fit rather nicely. Unless you try to install them with the K-member in place then they are a real pain. I have also installed JBA shorty and Ford Motorsport shorty headers on Cobra and GT 4.6 Mustangs and they are everybit as much a pain in the butt as the long tubes.
By far the worst set to install, even with the K-member out was a set of Sean Hyland long tubes, plug the ground clearance was nil. This was 5 years ago and I hear Sean Hyland has changed suppliers since then. They were by far the BEST sounding headers I have ever heard! But it was a lot of pain and suffering just for the sound quality.