yes the LS and X-type heads are unique castings...I know, I work in the plant that makes them. Used to be Ford, now is a third party. We make them using the 'Low Pressure' casting process (metal is injected with air into the bottom of a semi-permanent mold).
The Duratec 2.5L and 3.0L heads are made by I believe some company in the US called Tekshead.
The heads DO look alike but there are a few casting differences and definitly a bunch of machining differences.
For anyone seriously building an engine, why not just port and polish your stock heads... you'de get better results.
