Here is a method to unstick a frozen engine that I thought I would share with you. It is not my method but from a guy named James Monroe. I read it on another forum for old cars, then I asked a chemist friend for his opinion, which follows:
"Drain the crankcase. Through the carburator neck, pour drained out motor oil. The worse, the better! Fill the engine. Remove spark plugs to let trapped air out. Put the plugs back in. Take the exhaust loose at the outlet and plug it. Go by the engine each day and top the oil off with more of the same. Drained-out motor oil from a diesel seems to work more quickly. You will find that the crankcase is filling. That is the oil getting past the rings. It takes patience, but after a month or so, you will find the engine will turn without excessive force. Clean up the mess you have created, turn the engine over a bit to clear the oil from the cylinders, replace the spark plugs and start it up. You won't be able to see the house or shop for the smoke, but the engine will clear up without stuck valves, rings or lifters. Most of the great guru's don't believe this. That is because they either haven't tried it or left out a step. Fresh motor oil will not work, period. It must be contaminated with acid ect. On a Model A engine, of course, you will have to fill through the spark plug holes. If you follow these steps I have outlined, you will swear by this method of unsticking engines. "
Now the chemist's opinion:
"From a chemical point it makes sense. The S (Sulfur) in gasoline and diesel fuel burns to SO2 and SO3 (Sulfur dioxide and trioxide) during combustion. Add water (also a product of combustion) and you get H2SO3 and H2SO4 Sulfurous and Sulfuric Acid. Also explains why the used oil from a diesel works better, much more Sulfur in diesel fuel.
Beside the Sulfur products, there are various other acids, Nitrous and Nitric for example.
I would recommend adding oil through the sparkplug holes to cylinders that do not have a intake valve open to admit the oil from the intake manifold. "