Can someone who knows what they're talking about on a Ford big block please help me?
I'm new here and this is my first post I don't even know if anyone is around?
I am a chick but I can keep up pretty well if you lead me in the right direction.
I have a 1986 E350 Ford Econoline cutaway Motorhome.

It was sitting for years and years and only driven a little bit.
I am trying to overhaul it.
I replaced the spark plugs and I sprayed seafoam deep sleep inside of the cylinders to lubricate.

I replaced the starter
I have a new battery
And I bought a new solenoid from Amazon

Changed all the fluids and trying to start it now for the big moment..
But...
No matter what, when I turn the (loose) key in the ignition, the starter cranks two or 3 times and dies down.
Like, it gives up. Seems like it can't handle the effort.
The first I thought it was just a battery and I tried jumping it to another battery for added juice. I then went and bought a brand new battery.

No matter the cranking amps, it's doing the same thing.
I took the starter off and realigned it.
I can turn the engine manually although it is pretty tough to turn with a big breaker bar even.
I tried to turn the flywheel with a big flat head screwdriver and I really couldn't even get it to move.

But I did see the flywheel turning when I manually spun the engine at the crankshaft.

One more detail, don't let this scare you though..
So, I power wash the s*** out of the engine one day and covered the distributor and the carburetor and some electronics.

But later, when I decided to pull all my plugs out one of my cylinders was entirely full of water.

Water did sit on top of the engine for a while. And then I saw that my valve cover gaskets were pretty loose.. could that have been the entry point for the water in one cylinder?

I turned the motor and the water drained out.

​​​​​It kind of freaks me out how water got inside I'm hoping it's just from the power washer. The vehicle was pretty low on all fluids so I do not think it was coolant.
I get an oil change and there's not creamy oil but there was water that drained out with some of the oil at the beginning


Having said that,
What would you do next? I have checked my ground to the engine and it all seems okay.
Is there some kind of bypass test I can do to single out these components?

My main concern is that the engine is too hard for the starter to turn because of some kind of rust buildup or warped? I dunno can someone please chime in 🙏🙏🙏. Thanks..Victoria.