Update. It spins! I unstuck it. Took the engine out of the frame, removed the head and cylinder. Placed engine on workbench forward end facing up. Soaked the crank and con rod bearings with PB Blaster. Was able to move the con rod back and forth a tiny bit. Then more. Then quite a lot. More Blaster and some of my precious supply of Silikroil. And whammo. Now it rotates freely, round and round.
What kind of engine oil are these Minarelli supposed to run? I'd like to flush the insides with an oil change or two. Then put it all back together and see what's what.