IIRC the mounts are different in a Focus vs. a Puma/Fiesta.

ECU depends - is your Focus engine a black-top 'SE' or a metal-cam covered 'S'? If you change between the two you will need the new engine's ECU and loom. This is because the SE uses a combined air temp and MAP sensor in the plenum near the throttle body; whereas the S uses a MAF. If you change ECU, you will also need to change the GEM or CSM (depending on what's in your focus - unfortunately 2001 was the year everything changed so there's no way of telling without looking!) and the immobiliser chips in your keys.

Chris