I have twin JD 4045s. In my first 1,000 hours, I lost both raw water pumps. I suggest having a new or rebuilt raw water pump ready to install. I installed one while underway across the Sea of Cortez. It is a LOT easier than changing the impeller. Then, when you're at dock you can have the water pump rebuilt and ready as a backup.
The first one that went out was under warranty and it allowed for a new replacement as a back up.
You'll also need plenty of Racor filters, 30 micron, and enough engine oil/fuel filters and oil to change out two or three times. I say 30 micron because JD insists that using a 10 or 2 micron filters will burn out the fuel pump.
Ditto for your NL... I lost my water pumps on my current Westerbeke and my prior NL.
You might have to clean out your heat exchanger if your impeller is chewed up.
Because of my travel in remote areas, I carried far more spares than I needed and I still have them in the box. If you carry a spare raw water pump and the oil/fuel filters, you should be OK.
currently lying Washington DC