After playing WFRP3 for a few years I started thinking that the 3'edition system could be nearly perfect for the Call of Chtulhu rpg.
Campaing specific careers could be easily created (and printed thanks to Strange Eons) and many social action cards, scarcely acquired by players in many wfrp groups, could become really appetizing.
Even monsters' conversion wouldn t take a great effort. Do you need a Night Gaunt? Just pick a Fury Demon and change the name!
The sole mechanic should be modified would be the sanity one.
It could be created very similar to the wfrp3 mutation threshold.
Every time your insanity points surpass the threshold (=to willpower+5 for exemple) you get an insanity.