When I removed the Chris King headset from my '93 Trek 5900 for servicing I hoped to reuse the existing CK crown race with an inexpensive Origin8 headset that I planned to use temporarily. No go. The angles don't match. So I had to pull the CK crown race and use the Origin8 crown race.

The crown race isn't really a conventional "race" since it only supports sealed bearings. But the angle still needs to match. It wasn't even close between the King and Origin8 bearings.