I guess the 4JH57 is a common rail engine which has CAN J1939 interfaces. I plan to do the same with a 3JH40 engine next year and did some research
Apparently Yanmar offers the N2K interface. I got hold of a parts
catalogue of this engine and in there it suggests the ECI-100 of Raymarine
to convert from J1939 to N2K. There are detailed schematics and part numbers of the cables
that would be required.
I can attach a picture of it later on (don't have it at hand right now).
In addition to this there is a post in the Raymarine
forum about it. Just Google
That being said I did the research
for the 3JH40 but I guess the 4JH57 is not so much different when it comes to interfaces - no guarantee though.
The ECI-100 manual refers to the 4JH57.