Still, I like the way that a simple dice-plus-adds formatted bit of information can be used to represent more than one detail. Plus, I'm already violating the original rules one way by using a Target 20-ish "add the character's hit dice to the die roll" approach. So why not reinterpret the way monster hit dice are used?
That's pretty concise. There's one other thing I want to do with that "adds" figure, but it's kind of tied to some other ideas and will need a separate post.
Monsters are rated in terms of "hit dice" (HD) and "additional bonus hit points" ("adds"), written "HD+adds". Roll a number of six-sided dice equal to HD and add the "adds" number to the total to get hit points. When the monster attacks, add the HD number to the attack roll as an attack bonus. When rolling damage, add the "adds" as a damage bonus. When rolling to see if a monster breaks morale, add the "adds" as a morale bonus.