Nothing, unless you get another one.
CC:
I doubt that anything is going to be a direct replacment except another Perkins. Even the different models of Yanmars over the years are different than the previous model.
They are several good choices out there so get prices on a "complete" job including prop, shaft, strut (if needed), wiring etc etc. Many times the engine/transmission combo will cost about the same as the labor & misc. materials.