Okay, I think I figured out a flaw in my plan... The portraits are REALLY hecking big. Each portrait consists of 9x10 tiles which aren't placed in order, of course... I'm not really sure how to advance from here, I can't even find a single tile relating to one portrait I'm looking at amongst all this mess. I'm using YY-CHR, the 2019 build, and I can find small spritework, but not the large portraits in the game. They're just too big to differentiate from each other.
If I could look at them all using the color palettes from the game, it'd be one thing, but every tile is shown with the same color palette, so differentiating between them is near-impossible...