Well you could go to the OMC dealer and check into buying all the parts needed to convert it over. Or you could check online for a conversion kit. Maybe Barr or Osco would have them. But I have to tell you many of the I/Os I see are not fresh water or heat exchanger cooled. The system will last about ten years running in salt water before having to change out exhaust elbows or manifolds. And if you flush out the system with fresh water after each use (you can buy a kit if your engine doesn’t have a hook-up or if you trailer it you can get a flush out to hook on the lower unit) it will last much longer. Think about this before rushing to spend for a heat exchanger system.