Most problem for fitting the FRS engine in another car might be immobilizer and OBD-2.
But it's not a hard job to fit the engine with an aftermarket management into any Fiesta.

And yes, Duratec ST engine fits fine into the MK6, but you'll need the gearbox also. It's called IB5+ because the Duratec is a Mazda engine with a different pattern for the gearbox bellhousing.