64 Fury

I think I'll try a little PB Blaster first, and if that doesn't work I'll hit it with the MM and let it soak for a week. It's a little strange, there is no evidence of water damage anywhere, no water in the oil, plugs were clean, carb looks fine, parked years ago and it's locked up
I use ATF, a dab in each cylinder for a couple days.

Keep in mind, moisture from the air can get into cylinders of engines simply due to condensation as the temperature changes. Especially when the rockers aren't removed to allow the valves to close during storage