I did use muratic acid. About, four doses with a Q-tip with the cylinder heated. Some 400 grit, and Wigglesworth Scotch Brite method.Next time use acid. It won't remove the plating like sanding can.
Provided you don't have gouges above the exhaust port you will probably be ok.
Stihl 661 cylinder and piston kit can be had for $289 on Ebay.
I've likely done 100 of these. This much transfer requires a lot of work. And, if you leave just a little it will get in a ring groove just as sure as the world.
But, all advice is appreciated.