Yes, let the solvent sit in the cylinders for a few days and then try to turn manually. Can you get a socket on the crank snout bolt? It would be much easier than trying to turn it with the ring gear. Try it turn a little-forward and backwards. Go easy on it. If she breaks free, put fresh oil and filter into, and with spark plugs out spin with starter motor to clear cylinders. If you have an oil pressure gauge, this would be a good time to see what pressure she pumps. Install plugs and fresh fuel and try to start her. Keep the RPM's low until you are sure of engine condition.
Don't forget, the backwards engine will have a reverse rotation cam, so don't get them mixed up if you have to tear them down.
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