The shop I worked in Oz had a J.A.Stein knurling tool to enlarge the crown race seat. That was in the days of loose bearing headsets and a split crown race was generally considered a bad thing.
I am not sure how a split crown race helps the situation unless it is on a tapered seat or the tapered bearing doesn’t bottom out on the split crown race.
The shop I worked in Oz had a J.A.Stein knurling tool to enlarge the crown race seat. That was in the days of loose bearing headsets and a split crown race was generally considered a bad thing.
https://steintool.com/portfolio-items/knurling-tool/
I am not sure how a split crown race helps the situation unless it is on a tapered seat or the tapered bearing doesn’t bottom out on the split crown race.