Pour a couple of ounces of Kroil or some other penetrating oil on top of the pistons and let it sit for a week or so before trying to move the crankshaft. I've heard a mixture of acetone and ATF works well, but I've never tried it. Kroil is made right up the road in Nashville, and I've usually got a gallon can of it sitting around the shop.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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