The first generation known as phase 1 had a metal cam cover scribed with Zetec-S, the later phase 2 engine had a plastic cam cover with Zetec-SE printed on it. They are both the same engine to all intents and purposes and are interchangable it's just the phase two has some internal differences like valves etc.

The same engine can be found in the Fiesta Zetec S.

Martin