In general, I've resisted the urge to write player character versions of our monsters for old school D&D (and/or Labyrinth Lord etc). The Company of Monsters was supposed to be the game where you play the monsters. HOWEVER! At this point I think I've got a decent framework to make monster templates for use with The Nightmares Underneath, composed of marks of heritage and abilities like those you get from divine patrons (both from The Nameless Grimoire).
Here's a first draft of the rules explaining monstrous professions (there are 4 professions here, but I have ideas for a few more). These are like normal adventuring professions in The Nightmares Underneath, but instead of a full suite of special abilities, you get to take monster powers from your monster type template. So you end up more "monstrous" than you would if you had a normal profession.
Of course that means now I have to start writing up the actual templates, for monsters old and new.