The best product I have seen yet, to free up rings, is K&W Knocker Loose penetrant. You just have to spray some into each cylinder, and let it set for a week, then spray some more, and fire and go.
16 years ago, I used 4 "spray and let set" for a week times, then sprayed one more time just before cranking it over, in a 1950 flat head straight 8 Pontiac 2 door Business Coupe, that would not turn over by hand when purchased. It did not smoke, and still does not smoke, or use any oil now. Also the engine has never been apart, it's all original, 6 volt even.