Thanks for all the suggestions. I had already taken the engine apart and dunked the parts separately. The rod is free on the pin, and I've cleaned the exterior of the piston with a used scotchbrite pad. It had obviously been run for a while with stuck rings because the was a LOT of burned on blow-by below the rings.
I haven't had a chance to do anything with it since the initial post - just one more day in the anti-freeze. I'll first give it a go with the heat gun, then switch to the acetone.
The rest of the parts have cleaned up pretty well. The case finish is different from what I have ever seen on an Enya; it's very shiny, almost chrome-like. No sign it had ever been polished or messed with. That is usually pretty easy to see in the crevices and on the corners. It is the first version 60 7032.
Jim