Sean Hyland Motorsports is an excellent source for parts and info.
SHM website
buy his book
4.6L Ford Engines
This book lists all of the differences in parts for all 4.6L variants and states which parts are best.
You don't need the 03 cobra heads, they're not that much better than the 99-02 heads, not anything that a minor port job couldn't exceed. Anyhow, the book states flow numbers and is very informative
The 4.6 is an awesome engine and is a perfect fit for the Pantera!
It is a perfect starting point for a performance build. It doesn't have the short comings of the Cleveland. The Cleveland has a weak block and is just plain old technology. the 4.6 aluminum block from 93 to 99 can be prepped to take as much as 1500 horsepower according to SHM. The newer 00 to 02 blocks are good for apx 900 HP, and the 03 to 04 blocks are Iron and are strong as well. It's easy to get these blocks, heads, and the forged steel crank. I have 2 forged steel cranks and paid apx $250 a piece after shipping.
The biggest weak link for these engines is the connecting rods. The 03 and 04 cobra engine comes stock with Manley H beam rods. You can buy these rods for $500 and they're good for over 700 HP.
Anyhow, don't give up on this engine. It's nothing to be scared of and will be much more rewarding and impressive than an old shrimp boat engine
(that should raise some hate and discontent)Nate