The early engines had a metal cam cover enscribed "Zetec-S", the later ones were plastic and had "Zetec-SE" printed on them, these are known as phase 1 and 2 engines respectively.

The engines are the same, phase 2 engines had slight enhancements in the head but it's still the same engine none the less.

The Fiesta Zetec-S model, again used the same engine borrowed from the Focus.

These are "Throw away" engines, i.e. due to the design of the engine block with a ladder style crankshaft iirc you cannot rebuild them.

Martin