There are any number of tricks for freeing stuck pistons in an engine which has been sitting idle for a long time. Most involve putting a penetrating oil in the offending cylinder and periodically tapping it with a hammer handle or a 2x4 used as a drift. Some folks with the means to do so immerse the entire engine in a barrel of diesel fuel for a few weeks before starting disassembly. Grandpa's #1 and #2 were beyond any tricks I performed.
The ultimate approach is to beat, chisel, drill, saw, and/or grind out the offending piston and the rings. The rings are usually the real problem, being rusted to the cylinder wall. Be careful of the cylinder walls and rods if you plan to reuse the block or rods. Drilling out one half of the piston skirt, cutting through the rings in the process, and splitting the piston head in half usually frees it up enough to drive out. However, even though #1 came out that way, #2 had to be split down both halves and even then was hard to loosen up with a heavy hammer and drift. It may be hard to see in the photo, but in real life, when a piston is cut out like this it is easy to see how the wrist pin is offset in the piston rather than in the center. In this case, it is the right side of the engine so the wrist pin is offset away from the valves. This is why it is important to make sure the markings indicating the front of the piston are pointing toward the front of the engine during a rebuild.
With the piston driven down to loosen it up, you can see how much was removed from the piston. Notice how the upper half of the piston skirt broke off at the lower oil ring land exposing the steel piece embedded in the piston. (Could you follow that sentence?) Also, notice the aluminum chip "snow storm." What a mess this makes.
Once the #2 piston was out of the way, a big crack was revealed. I drew a clumsy green loop around it to help you see it. I would guess it was caused by freezing water. Depending on what else turns up, a sleeve might save the day, but a real mechanic might have a different opinion. Regardless, it will have to wait until I'm a little more desperate for a block. Of course, I might just get sentimental.