RE: Crashed in water
Another thing to look at (after checking the above) would be valves. I'm thinking that they are rusted in place. Frank is right, disassemble the engine. Take the head off and see if the valves move. If so, you may have a fighting chance of saving the engine.
If the engine wasn't run out as Brian suggested, it may just be a giant chunk of rust inside. There is only one way to find out for sure. Personally, I'd give it a go. I'm betting that this engine can be brought back from the dead, but not just by filling it with fuel and trying to get it to fire. You may be doing more damage to it if the valves are rusted/stuck.
Just my $.02