The length is fine. no need for a longer/shorter nut. It was the diameter of the shaft that was preventing me from mounting my brakes.

However, I was able to get the nut in with some... encouragement (light tapping with a huge rubber mallet). Probably not the best way to do it but it just seemed like it wasn't going in due to too much clear coat on both the fork and the nut. A few mild taps and the nut moved into place. Would rather have the nut drop right in but that never happened. Inspected the fork aftwards and it looked the same, no bulging, chips, or cracks. I'm not going to worry about it.

Thanks for all the suggestions.