As advised, I removed the muffler and peered in at the piston. It had a small discoloration in the exhaust port, but seemingly nothing major. Still, there was a significant scratching noise as I rotated the flywheel.
Finally, I concluded that I could not remove the head without first removing the gas tank, and the screws holding it were obscured by the flywheel. So I wrestled the flywheel, for about an hour. Tapped the rim with a hammer, and squirted WD40 around the shaft. Finally, I made up my own flywheel puller from a piece of angle iron drilled to accommodate the two bolts that hold the starter pawls to the flywheel. Used these bolts to attach the angle iron over the center of the flywheel, then backed out the main flywheel central nut to press the flywheel off. Nothing doing. So I held an 8" piece of 1 x 2 against the back of the flywheel rim, near the thick sections that hold the magnets, and tapped on the end with a hammer. No dice again. Well, it had to come off, so I went back to cranking on the central nut - and, lo and behold - the flywheel fell off in my hand.
Behind the fly wheel were three bolts that hold the fuel tank to the crankcase. Two of them had rattled loose, and would have fallen out if not for impinging on the back of the flywheel. Tightened them up, and observed that the scratching noise had disappeared (!).
At this point, I could have dropped off the fuel tank, accessed that fourth bolt, and removed the head; but assuredly I would have needed a new gasket for reassembly, and it seemed asking for more problems. So I declined the opportunity, reassembled all the components, added fuel mix and bar oil, dripped a teaspoon of fuel into the carb, and pulled the starter cord. Ignition! She's been running like a top since.
Thanks for your interest and advice.