Hi and thank you for your question.
The first thing you want to consider is how much money and time do you want to invest in getting the bike running again. This is a decision only you can make but understand parts for repairs could easily exceed $1000, and quite possibly double that, depending on exactly what the problem is.
As far as dumping Marvel Mystery Oil into the engine, or running it through would entail filling it and quite possibly fabricating some sort of adapter for the drain plug hold to connect a hose. I would think you would want to loop it up high enough to ensure the crankcase is actually full. Understand that when the engine has the proper oil level, it is no where near full. The crank does not run in oil, nor do the cylinders. As far as the mystery oil itself, I am not a big fan of that. This whole procedure doesn't seem like a tremendous benefit vs. the probability that it might work and what you will end up doing if it doesn't. It surely won't hurt anything but I am skeptical as to if it will work and how long it could take. I am a bigger fan of getting my eyes on the problem ASAP and going from there. If the cylinders are full of rust, you probably have your answer.
To diagnose it and get a better idea of what you are up against, I suggest removing the cam shafts and cylinder heads. Look for rust in the cylinders. If they are rusted, you will need to soak them down with penetrating lube, probably a couple times a day for maybe a week, depending on how bad they are, until you can get the engine to turn over by the crankshaft. Providing that works, the cylinder walls need to be inspected for pitting. If they are pitted, they will need to be bored out and oversize pistons installed. The next problem you may run into is parts availability. I just looked up OEM pistons for an 1100 Wing and they are no longer available from Honda. This doesn't mean they can't be sourced aftermarket, like Wiseco or some other aftermarket manufacturer, but keep that thought in mind that you want to try to get a complete estimate of everything you need, before you start buying any parts. There would be nothing worse than getting almost completely done with the engine and finding out a critical part is non existent. Also, the crankshaft could be the source of the problem as well. Again, that can be extremely expensive to repair as well. It is not available from Honda as a new part, but depending on how bad it is, there may be companies that can repair it for you.
I would suggest getting yourself a service manual so you have a guide to disassembly and assembly too. I got one for a 6 cyl Wing off Ebay once so it is something to think about. That is one relatively small investment that I would consider an immediate necessity if you want to attempt this project. If nothing else, it should be fun to take it apart and learn a little about how the wing engine works.
If you have any more questions, feel free to ask.