The engine on the BS-7 was a bit stuck, so I had been soaking the upper end in penetrating fluid for a couple weeks. Thanks to a little mount I built, I was able to have the engine sitting "piston up" on my work bench. And luckily, the piston was high enough in the cylinder that the intake/exhaust ports were covered up, so the penetrating fluid was able to do its job.
I was able to move the cylinder a little bit by hand, but I needed a little bit of persuasion from a simple puller tool. Thanks to the longish cylinder studs, I was able to pull up on the barrel using a gear puller. I was very careful not to pull up on a cooling fin, and instead used the beefier intake and exhaust port castings:
Success! Don't be fooled by the color of rust, the cylinder is surprisingly free from corrosion and scratches. I think it will hone quite nicely. Also, the piston is very clean too. The piston pin clips are a bit corroded, so I'm soaking them in fluid too. I'm thinking a set of clips from a Honda 50 engine will work as a replacement:
The engine isn't entirely "unstuck" yet though. The connecting rod only moves a little bit with light pressure, so I'm assuming the bottom end has some corrosion issues too. Which is somewhat surprising, as the oil I drained out of it looked perfectly clean. It looks like this engine will require some internal work to bring back to life.