Most everything that would need touching will be touched while putting a new engine in.
Don't try and use the old gas. Empty the tank and put fresh gas in. Varnished gas will stick a valve and your new engine will turn to junk. I've watch it happen twice and know others who learned this lesson the hard way. It is so tempting to run the old gas (as it will run on it). Adding a little fresh gas doesn't fix the problem. There is a good chance the pump is junk from sitting that long as well.
Knowing my luck its got a full tank. Could prob put power to the pump and get most out then drop the tank and try my best to clean her out. Going to try and get her running this week. Got a lot of work to do.
The problem isn't water in the fuel. It is the fuel itself going bad. It turns into a varnish. Stinky and orange in color. It will literally stick metal parts together, like valves into the valve guides, rings, stuff that touches fuel.