Post scriptum: I'd also have a look at how To Hit Bonus for monsters gets determined.
In the combat chapter it's stated that Momsters add their level, but nowhere can I find how a monster's level is determined. This is especially important for creatures with less than 1 HD or bonus hit points.
Going by what I posted above, a Monster should have a Hit bonus equal to HD-1, with a minimum of 0. Adding 1 if the monster has bonus HP.
But the simplest solution to it all (including my previous post) would probably be:
Leave Class To Hit Bonus as they are, starting from +1
Add a monster's full HD bonus to attack rolls, minimum 1, +1 for monster's with Bonus HP.
Start AAC at 11 (yes this means checking all instances of AAC in the rules, with AAC=20-DAC)
