Maybe just let it really soak with the good penetrating oils sprayed in and wait for a few days for it to work; maybe less damage to cyl walls and rings that way...
On mine it took me a few days to figure out my no start or slow start really bad running was water in the cyls not a tune up issue. So the salt water could have been in it maybe 2-3 days. Once I figured that out (boat was on the mooring), I drained the block and manifolds and repeatedly fogged the heck out of the engine. Then when I got it home, did some tests which verified the blown HGs. The water definitely did not come from the bat wing manifolds because I tested them with acetone.
I was always able to crank it over by hand. In fact I did not use the starter till I got the heads back on. When doing a compression test with the plugs out before I took it all apart, I was able to turn it even by pulling on the drive belts wearing heavy gloves, so I knew there was not likely corrosion damage in the cyls before I took it apart.
I also thought about bearing damage due to water in the oil. I did have the milkshake under the valve covers and intake manifold. I took out all the hydraulic lifters and looked at the lobes carefully. They looked really good. So did the sides of the lifters, no rust anywhere. I used the Merc oil for some years, maybe the business about better corrosion resistance than regular car or HD diesel oil is not BS.
If you had a milkshake under the valve covers you might want to get that out of the pan, it is harder to pump it out when cold esp mixed with water. I used a heat gun very carefully with an IR temp gun monitoring temps, (like no more than 150*) to heat the oil so could get it out even though I could not run the engine. Changed it probably 4 times. After I ran it on the hose all finished the oil is perfectly clear and clean.
Good Luck Tony I know what you're going through. Let us know how it works out. Just give the penetrating oil time to work.
More to come......
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