The 1.8 and 2.0 Zetec E are very similar, heads can be interchanged etc. The 1.6 has a different head iirc as the bores are a fair bit smaller.

The 1.6 Zetec S engine is totally different altogether though! So dont know where you'd stand with fitting a any of the early/late zetec turbo kits. An obvious difference is on the Zetec S series engines, the intake is at the front, the traditional Zetec engines have the intake at the back.

Mind you, its not that hard to do from scratch really, turbo, manifolds, engine management, injectors, intercooler etc.