Sometimes there can be something other than the pistons that are frozen. A couple of years ago I started to take apart a 261 that had been in "storage" (twenty years outside under a tarp, then 22 years in a garage) for 42 years. A little WD-40 loosened the pistons, but the camshaft bearings were frozen and the crank would only rotate within the backlash of the timing gears. I made a tool to apply torque to the cam (with the crankshaft gear removed), and after a couple of weeks of penetrating oil and torque application, the cam finally broke loose. I have also seen oil pumps freeze up.