03/04 cobra head ?

The heads are very close to the FR500 head specs on the exhaust side, and actually slightly outflow them...they don't flow as much as the FR500's at low lift on the intake side, but they flow just as well as them at high lift...

You should get the Sean Hyland 4.6L Engine building book, it has all the info in it that you need about the 4.6/5.4L engines...Amazon.com has it for about $14+shipping