Thanks for the suggestions. I suppose I should add that none of the spark plugs were rusty at all when I pulled them, so i hope that means the rust is just the usual stuck rings and surface rust in the unsealed portions of the engine. I will be rebuilding this one, but will keep trying at this point to unstick it as having it running, even a little, will make loading/unloading etc. so much easier. Will pull a valve cover to get an idea of the inside engine rust.
I have successfully freed a stuck engine using used diesel engine oil. Filled entire engine, let sit for a couple months. Results may have happened sooner, only couldn't get back to it for that long. Running like a top today.