Well, I didn't actually let the grinder eat it, just let it nibble a bit. I took the jug off and scribed a line on the exhaust port to match the gasket. I then took it down to that line with a dremel and did my best to feather it in and polish all the marks out. I was mostly successful, a few gouges didn't quite polish out. The best thing about the whole experience is that when I put it back together, it ran again, at least for the moment.. My tach is out on loan, I suppose I'll let it sit till I can confirm what it's running at.
Ian
Ian