Okay to use a wire-brush on angle grinder to remove rust?
I'd use my drill-mounted wire brushes on the outside.  I've got a range of shapes and the slower, speed-controlled drill would be gentler on the workpiece.
For the inside, I think you'll have to do it by hand.  Steel wool wrapped round a dowel, or better a piece of 2x1 planed down to to an oval that fits freely inside the hole, should do the trick.  If you use enough steel wool you can wrap it onto the end of your stick and staple/nail it in place