Take your time with it. Use diesel fuel, as it will soak past the rings easier than ATF will. If the head isn't off, I'd take it off. Keep the cylinders full of diesel fuel for a week or so. PB Blaster should work, but will be co$tly because you will need quite a bit of it. Then, as Josiah suggested, try rocking it. Also try your 5# sledge hammer, using a large piece of wood on top of the pistons, not getting too carried away. The 235 that was in the '51 was stuck when dad got it. He used this method, and it wound up running just fine. Just make sure the cylinders or rings aren't pitted (they shouldn't be in that short of time).
