I think I would save the trip to the John Deere dealer. There are no Perkins used in John Deere products. After 40 years with Deere I hunk I know what I'm talking about. Deere builds their own engines except for Yanmar power small engines in compact equipment and Kawasaki power in lawn equipment. Old lawn equipment had Kohler power, and a few have Briggs and Stratton. Perkins was used extensively in Massey Furguson equipment. Perkins did/does make fuel injection. That market is controlled by a handful of injection brands. CAV, Bosch, Lucas, Nippondenso and possible a couple others. I would be talking to a diesel fuel injection rebuilder. Not necessarily a boat service guy, but rather a truck, ag and industrial provider.