For some reason, I became confused or missed that (important) detail. It must have been all the switching back and forth between this guide, the hairstyle guide, and various other posts in my quest to quickly absorb as much relevant info as possible. The fact that it working in wowmodelviewer didn't help either.
In any case my NightElfFemale -> ScourgeMale conversion has gone very well. I have the face/skin color combo I want, a proper jaw, and the proper hair and hair color.
The things left on the todo list are:
-Figure out why the NightElfFemale chest is still there! o.O
-Figure out why the eyes and eyeglow are not showing up.
-Figure out facial/scalp features. Luckily my original character had no features and my edit turned out the same. But I would still like to know how to do this for the sake of knowing and possibly helping others achieve their desired look.
Thanks for the guide!