Thank you very much for your comments.
Gabriel, I used a checkering file to do that. It is a rectangular file with 10 teeth per inch. (correction: 20 tpi) It is simple but tricky on some shapes to file. In addition to some shapes being awkward, I always try to file all of the spacers at the same time, by pinning them together and cutting through all of them, in this case just two. That way all of the teeth match and line up. On multiple spacers that are not the same size, I find a starting point that is common to them all, start there and flare both directions. That doesn't sound very clear, but once you see it, you'll know.