I think I'd try more of the ATF and acetone in the cylinders and then drain and replace the oil before trying to crank it over - just some cheap oil that I would drain again soon after getting it running if that ever happens. Sorry to say it but I'm also in with those who have their doubts about it just shrugging off being seized up. If it doesn't spring back to life, I'd drag it into a barn or build some kind of cover for it if you are going to try and repair the engine. I've seen pieces of equipment sit for a long time and start right up but the engine hadn't seized. Maybe the can on the exhaust blew off and was replaced later on? I use a 5 gallon bucket on the exhaust and secure a tarp over it if the machine lives outside. It's a PIA to cover and uncover every time you want to use it but it avoids the big problems like this.
It doesn't take a year or more to have water get in your exhaust and ruin your engine, it can happen overnight. If water of any quantity gets into one or more cylinders and you try to - or even worse succeed at starting the motor - it's going to be trouble. Make sure you have the spark plugs out when you are trying to crank it or pull it if the cylinders are full of your rust buster potion.
It doesn't take a year or more to have water get in your exhaust and ruin your engine, it can happen overnight. If water of any quantity gets into one or more cylinders and you try to - or even worse succeed at starting the motor - it's going to be trouble. Make sure you have the spark plugs out when you are trying to crank it or pull it if the cylinders are full of your rust buster potion.