I don't think Grievous is vulnerable to the weapons in the hands of the assassins. Remember his battle with the Gungans? How many pikes speared the General? Ion weaponry may be effective (again looking at the cheating ways of the gungans), but would Revan know to use it? Probably. Grievous did still put up a fight after taking several Boobas(funny word ) to the face!
This is a challenge, but I wonder if a projectile weapon could puncture duranium. Not much is said about it on wookiepedia. They might be a to use ion weaponry-but I don't know the effect that would have on Grievous. Or use explosives. The heat might become high enough, or the shock wave might kill him.
I don't know about explosives. He's survived quite a few explosions.