By CRX I presume you mean the Daystate CRX?
With the CRX I can only think of four manufacturer variants:
CRX-MM - Made out of titanium, very expensive, only seen one.
CRX-ST - Think this was made for the USA market, made out of steel. Trev Ryan and myself have a couple of ST breech blocks on our CRX's.
CRX - alloy, have heard of a couple of these being made by the factory.
CRX, standard steel version. Some have been fitted with the lighter hammer from the CR97SE.
As a side note there are a couple of CRX's converted to electronic versions - think one was nicked though and went missing, 2 Zenith rifles, that I know of, made by Nick Murphy with CRX trigger units also I am having a custom built rifle made that will be fitted with a CRX-ST breech and CRX trigger unit.
Hope this helps.