If the ZD30 is any good why did you want a spare engine?

Personally I think most, but certainly not all people who do a conversion do so because it is an opportunity to offset rebuild or repair costs against the purchase of an engine that is more reliable or more powerful or whatever other quality they are chasing.

Lets face it, a ZD30 isn't exactly a good performer in a Patrol.
I had a CRD for 5 years (one of 6 Patrols I have owned) and I quite like it but it didn't have the reliability or torque band of say a TD42.
If it had of crapped out from say Pump and Rail and I had of wanted to keep it I certainly would have converted it rather than reco the ZD30