Hello XXXXXXXX, salt water is the worst scenerio when it comes to engines. I have seen success by filling the cylinders with marvel's mystery oil or fill the cylinders with rust penetrent like WD40 and let it sit for several days. From that point try very slight movements of the crankshaft in both directions until you start getting movement, then let it sit again for a few days. Keep this process going and keep refilling the cylinders. It should free the engine up and hopefully you won't have any ring or cylinder wall damage after.
Your JA Expert,
Ivan
ASE Certified Master Technician
ASE Master Tech w/ 19 years in the field. Self employed for 9 years. Member of AUTOLAB radio show.