The only other thing would be to take out travel insurance that would cover a misconnect, however 8 hours should be sufficient.
Insurance which covers misconnects will not be sufficicient here. OP needs "all perils". He is not connecting at JFK, but rather terminating one itinerary and starting another. Thus, he would be a no show for the x JFK, the same as if his taxi got in an accident on the way to the airport.
Eight hours is enough, unless it isn't.