Back from work this morning, so after a snooze because of a night out of bed, I pressed on with preparing some more ribs. 14 now complete, so halfway.
The ribs with XXXX-L name have been pressed out so that the burrs are on the outside, making them easier to remove with the grinding wheels. But those with XXXX-R, ie flanges on the right side, are the other way round. So these inside burrs have to be removed with sandpaper.
I find that small strips of 320 grit cloth-backed sandpaper cut from a Norton Handy Roll work well.