Freeing up a frozen block ??

I learned a lot as a kid from just taking thing apart. The harder it was the more fun it was. I think it is still fun to take things apart, unfortunately the wife expects me to put them back together again, nuts.

jos51700 is exactly right, this is really good practice for when you might really need it. Almost any kind of penatrating oil or liquid should do the job. It just needs to be low viscosity to actually soak into the rings. Frankly I'd start with either the cheap and easy options of gasoline or diesel fuel. But as a last resort you could always just take a chisel and break up the stuck pistons and remove them in pieces. If you were really going to save this engine, you would have to bore it out oversize so the pistons in a rusted stuck engine are useless anyway.

One other place to go for ideas on this kind of project are the tractor restoration websites. Those guys run accross this all the time, and find amazing ways to unstick the engines, and they have the harder task of saving the pistons since replacements are usually unavailable. They do have the benefit of only needing the antique tractor engine to run up to about 2,500 RPM with a compression ratio in the 5:1-6:1 range so the needed quality of the bore and pistons is much lower than a modern engine. They can sometimes still get them to run after sitting in an open field for decades.