I'm no expert by any means, and you may well be right on all other accounts, but I would just like to add my experience on this matter to the mix. I've sanded down two stems to fit French sized Peugeots and both times it took me no time at all with a piece of standard brown colored sand paper. I've also sanded down an alloy seat post once that was really close to fitting. Again, it took not much at all. It seems that aluminum is soft enough to take material off quickly even if it is a hard alloy. No need at all to worry about blistering hands. A file is Definitely not even close to needed. People say to sand it down because even sand paper is more than adequate. And so many have done this and so little material needs to be removed that I really don't think it's a safety issue either. Sand away, OP.