JonSpecB

Sadly I had a fairly catastrophic engine failure in my 2005 3.0 spec B last month. I have bought a replacement engine which came from a 2008 Spec B which seems identical except is from an automatic. Both engines are EZ30"R"s. i.e. plastic inlet manifolds etc. I am just a bit bothered that the original heads are marked Z30 (e.g. Z30 001 RH) whereas the newer heads are marked U30. Can't find anything listing these codes or suggesting what they mean. Does anyone know if there is any significance to those codes, are is just a date indicator? Thanks