I don't know what the Focus RS turbo is like size-wise, but the T3 isn't a straight swap either as it requires some mods to be made like moving the radiator forward an inch etc, Fords reason for fitting the T2 was due to the lack of space under the bonnet of the Fez.

Also the car would need to be mapped to suit the FRS turbo, as off the shelf chips (I.E 195) won't be calibrated for this turbo.

Martin