One process which I've seen work is pouring diesel in each cylinder and letting it sit for a week or so. Keep checking to see if it drains down. Work the crank with as long a cheater as you can fit under the car until it starts to turn. You might also try rocking the car after the diesel has done it's magic. Once it breaks free, just keep working it a little at a time until it turns like it should. I've seen some pretty rusted blocks come back to life so keep working at it and you might get lucky!