Barney,
I completely disagree with the above posts.
Listen to your friend, who knows what he's talking about.
What you don't want to do is attempt to turn the engine over if there is water in the cylinder. You can bend a rod, crack a pistion, crack a head or damage a rod bearing or crank (or both). What you don't want to do is force the engine past top dead center if there is a hydraulic lock from the water. If you don't know for sure that all of the water is out of the cylinder, then DON"T do it!
Also, how long has the water been sitting in her? If it's been for an extended length of time, then it needs to come apart for sure.
Without question, I'd take it apart to find out what shape the cylinders are in.
You'd hate to make the problem worse or create additional problems by being in a hurry.
Regarding removing the heads, you should just be able to undo all of the large nuts and it should lift off. It might just need a little persuasion with a dead hit hammer to break it loose. If you don't have a dead hit hammer, a block of wood and a regular 5 lb sledge will also work. Don't whale on it! Always make sure to hit the block of wood and never the head directly. Hit upwards on the head, down low near where it joins the cylinder if you can. For example, you might use a block of wood in an exhaust port and tap upward on it break it loose. Just make sure you have all of the nuts off. Keep in mind that it's hollow, so you don't want to beat the living daylights out of it. Often, the gasket has been sprayed with goop that sticks the head on. You don't need to be superman, but if you just get it started, then it will come off fairly easily.
Good luck,
Steve