If your 216 is 'stuck' maybe pull the Head and have a peek in to the Cylinders.
It's pretty easy pulling the Head on those, and probably, it would not hurt to get your Head re-built while you are at it anyway.
If you had got some Water/Rust in the Bores, and things are stuck at the Rings, unless it is really super 'bad' you should be able to get things freed up and cleaned and be alright again.
I went though this myself recently, and I would be glad to share notes.
