Whilst there are differences in the background, the bigggest being that DG is an illegal secret organisation as opposed to OV which is legal, there isn't much space between the two games. This meant that it was not really an issue to port from one system to the other.
The biggest difficulties I faced were that:
- CoC calls for quite frequent skill rolls so I had to use some judgement about when investigation points needed to be spent or not. BRP often requires multiple skill checks for a task whereas Gumshoe, particularly for investigation skills requires a lot less.
- the game was not structured in the same way as recommended for Gumshoe so it was not immediately obvious which were the core skills.
- the game called for Luck rolls which in BRP is based on POW to avoid an infection. There is no Gumshoe equivalent and although Health rolls probably would have been appropriate in this case, I just went for a straight roll with difficulty based on exposure. On reflection, it may have been better to get the players to do this but I wanted it to remain a secret. Open rolls may have ramped up player suspicion that something was going on but this way they all found out at once, eventually.
- no clear skill read across in a few cases. Gumshoe doesn't have skills for computing as separate from what you can do with a computer. It also doesn't have Physics (I allowed Chemistry).
- the shrink skill is too powerful as written for Cthulhu type games. This is easily fixed and can possibly even be used to set how gritty the game is to be.
- there seems to be an assumption under Gumshoe that PCs will find out the truth. With Call of Cthulhu I don't think this is the case so there needs to be an awareness of the fact that you might want to throw a ton of points against something but you sometimes will still fail.
Artifact Zero is not an easy scenario for the players but it seemed to work quite well and I enjoyed it. Especially when Paulo was shocked by the results of his calculations on how long his PC had to live.