Now I need help finding parts - or rather, an engine.
Once I got the oil pan off and heard rattling, I knew there'd be a problem. Sho' nuf, I not only found the decimated rings from the piston in cylinder 3, I found chunks of what could only have been the piston itself. Shining a light up in 3 confirmed it - the connecting rod looked fine but the lower 3rd of the piston was basically missing. The thin part around the bottom of the piston is the skirt, right? That's what the chunks were in my oil pan.
Luckily I saw a company that sells used G10's for 295, and they're up in Santa Ana, not too far from here, so I don't have to have the engine shipped. Thanks for the suggestion anyway, sbiddle, too bad it wound up confirming my worst fear.