As I suspected long ago, the romanized name form of 八木秀之 is
Hideyuki Yagi.
This
source is the first one that I find where it gives his romanized form. There are more sources (such as
this or
this other) where he is always mentioned as a flute teacher and that sometimes performs in concerts of classical repertoire.
Also, the mixing engineer that wasn't romanized until now is Yoko Uehara. Credited
in this album of the same year and under the same record company (Scrumm Staff). Also credited in our database (
here and
here too).