Chrysler Marine

[EPM 2]

Hi

Someone is trying to sell me a boat that has two Chrysler Marine Diesels. He believes they are Chrysler Nissan Marine Diesels. The numbers are as follows. Model Number mN633BCLX 164, Serial number E32915 7 - 019314 Part number is 2/3/78.
There are two engines but the second one had no tag on it. They are 6 cylinder engines.

Are they good engines, are parts hard to find. I understand Nissan has modified the cylinders by adding rings. Will the new cylinders work in the older engines?

Thanks