Lump it. Right now I got a Super Z in the shop where the engine model and spec label is gone. I all know for it is a CV740 or CV750. There is not even hp label visible so I would have do the same here by comparing parts. there is only 154 CV740 and 35 CV750 to choose from. Only which Super Z it is as the customer had record it before the label got lost.
Here a list of the X models as you'll see the 60" deck was only offered on the X2503 and X2703 mowers. So what may have been done someone swap out the decks. If that is the case then you will have to look at the X2503 and X2703 decks and compare the parts to your deck. Basically it become an informed guess as to which parts you will need.