I thought the first part of the chassis no. was the body style?
If so, would it not carry the same FN1/2 (can never remember which way round it is) as the TypeS 1.8 & 2.2?
Or have they changed the chassis with the 09 facelift?
It's all explained here Dave.
What does FN2, FK2 etc mean? - Civinfo Wiki
FN1: 3 door 1.8 petrol (Type S)
FN2: 3 door 2.0 petrol (Type R)
FN3: 3 door 2.2 diesel (Type S)
So logic says FN4 isn't a bad guess.