I ran into a similar issue years ago when I was trying to fine tune the AFB carbs on the Road Runner. I got the closest size over that I could and would use some sandpaper folded over and twist the rods back and forth/ and up/down with my fingers. I would check frequently with some calipers to monitor the progress and it worked out good. It is a bit time consuming, but I would just sit back in a chair and watch some TV to pass the time.