All the belt driven ancilliaries will fit, the ST170 engine is essentially a 2.0 litre Zetec with a funky head so all the fittings are the same.

I would advise fitting the ST170 power steering pipe, especially if using an ST170 exhaust manifold (standard shit one will fit to begin with though). I'm almost certain the standard plastic inlet won't fit the head ST170 head though (different port spacings) so you'll either need to use your 1.8 head to begin with with the 1.8 head gasket or knock up an inlet manifold somehow.

There's a few other minor things to consider but it's not an outrageously difficult swap. Wiring and ECU, if you go down that route, will be a pain in th'arse as well but, again, there's ways around that!