the sure fire way to free up an old engine is to get an old crock pot and pour some antifreeze in it, just enough to cover the engine. Turn on HI for about 2 hours. Carefully remove the engine with thongs and slowly start turning the prop.
Another way is to put engine in the oven at 200 degrees for about 30 minutes . remove and try to turn it over. You must use extreme care when trying both of these methods. I use the antifreeze method ofter, with no problems. BE VERY CAREFUL. And I forgot to mention, do not use the crock pot to cook in ever again.