Duratec Engine Number (UK)?

Before I bought my Ka, someone had changed the engine to a (2003) 1.6 Duratec Ford SportKA engine with X68E6090 stamped on the back of the engine, didn't declare it.
Can anybody tell me where the actual engine number is located on the block - only numbers I could find were 2003 1.6 X68E6090 - but this doesn't correspond to any manufacturing dates I have seen on the Ford charts. 2003 should start with a 3.
Been to Ford, they said they didn't know where it was either, any help would be appreciated.