The game is very much like DnD. most of the monsters could be used as is.
the gods listed are as avatars, and you could use them, if your party was able to take on CR 32 monsters...
The magic system is almost exactly like DnD, only there are no spellcasting classes or spell levels. If you know a spell, then you can try and cast it when ever you want. All spells have penalties for casting... as in sanity damage, and often ability damage or even drain.
A little bit of effort could be made to convert many of them.
weapon wise, they all work.
the rule set is closer to DnD then even starwars, so its very easy to convert one way or the other. You ever wanted to run a modern setting?
Have an evil NPC that was nuts and able to use evil rituals to generate magic despite not being a spellcaster? (I sure do!)
CoC d20 is very much like DnD with sanity issues. sure you may kill zombies... but you'll go nuts if you fight them often. Sure you can cast spells, but you'll go really nuts just trying to learn one.