Can't quite remember exactly now (about 2 years ago!) but there is 2 methods for detecting headshots in Kurok, depending on what kind of attack it was 

 I did one method for missile type entities, and another method for hitscan attacks. This alleviated most of the problem mentioned by Sajt, since most weapons in Kurok were of the hitscan type 
Can't be bothered figuring it out now 

 but I do remember looking into how it was done in the Matrix mod and the moddb tutorial page.