there is a topic in the re-store forum

the guy has put the i4 engine in a mk4

putting zetec in mk4 is easy cause u can buy all the bits to do it

work wise the 1800 zetec is the easy one to do u only need a new engine mount. it bolts to the mk4 box then u just have to wire it in (i think)

look in the re-store forum it will help u loads cause someone has done every thing to a mk4 in there

engines iv seen in mk4's are
zetec 1.6 1.8 2.0
24v v6 st24/200 engines
st170 engine

u could push the boat out and drop a 2.3 duratec in it