I would like to run Hunter: The Vigil with the God Machine Chronicle rules. Hunter has not yet been updated yet for the new rules, but how hard would it be to convert the rules a bit myself? The PCs in Hunter a pretty much mortal, so I am thinking the rules would follow the core book more closely anyway? Can someone tell me of potential issues I would run into by doing this? Thanks.
The book Mortal Remains contains rules for updating Vigil to 2.0 rules, as well as Dread Powers for monster types not covered in the other books.
Use those conversion rules.
The only real issue you would run into if you don't use the Mortal Remains rules is how to adjudicate Integrity with Hunters' ability to replace "morality sins" in service of the Hunt.