MDK- Marine Diesel Kubota. Last letter I guess is model, the MDKD is 8kW, Kubota D950.
MDJ- Marine Diesel J-series, that engine actually made by Onan. MDJA is one cyl, B,C,D,E,F are either 2 or 4cyl with slightly different displacements per cyl, can't remember which are which.
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