Knucks are a very bad idea to integrate into a PV, they are less legal to carry than guns in many states. You'd be better off integrating a spike or a knife blade, it'd be more legal in more places. Knucks have a pretty bad reputation as far as the law and would make you a target in the eyes of law enforcement whether or not it was legal in your state.
I'd say a "strike crown" type of
device would be about as far as you'd want to go with a PV.