Its the same fuel tank, its only the pump/level module in the top that differs. IIRC there is a driver module under the rear seat which controls the pump from the PCM (ECU). Unless they've added a new pump, the Sytec (Walbro) has problems with pickup of fuel at levels below 1/2 or 1/4.

That shows that there is even more to swap than just everything in the engine bay. Also, you could have problems if your current Focus is pre-facelift. The wiring is subtely different for those as the electronic modules are different (CTM, GEM, Hazards, etc).

You don't have to use ST170 brakes, but its a good idea as IMHO the standard ones are marginal on a standard 2.0. It does however need the front knuckles changing as well.

Martin