In the Mid-to late 80s I bought a 1956 Higgins 17' Speedster Utility that someone had repowered with a 225CI Marine Slant Six. It hadn't been winterized and the Cylinder head was externally cracked, and luckily the only cracked part. But it was stuck!
So I poured penetrating oil(probably the original K'nocker Loose back then, not the crappy PB Blaster clone they sell now) and took off head & cyl 3 rusty. So I cut down a 4x4 till it barely fit in bore and wailed on it till the piston moved & then moved slightly back and forth with big socket, just a little bit.
Then I used 80 Grit sandpaper(cheep ****) & sanded the rust off & vacuumed. Then I turned engine until I could see where rings sat & wiped & sanded that too. Then move up a bit & back down & wipe, multiple times.
Then clear to top backing down & oiling/wiping as I went. Left it @ top & did again later, basically got as much cleaned as possible
I then reassembled with junkyard head from Wrecks Inc & we Slalom Skied with it for several years. Higgins has smallest wake EVER. Great boat!
AND IT NEVER SMOKED! EVER!
Let the bitching begin!