The Range 4, 185 hp Perkins is a newer version of the 165 hp Perkins that was delivered with the venerable Mainship 34. It is a solid engine with no real vices. 1,700 hours is nothing if they have been operated and maintained well.
Trans Atlantic Diesel is your best source for parts.
You might find manuals at boatdiesel.com's pdf library, but you will have to join for $25, the best money you spend on a diesel.