I have the same reservations about the VN1500 radiator. As the Vulcan us rated at 64hp. I am used to having to upgrade cooling with horsepower. A radiator good enough for a 250hp 6L won’t cut it for a 500hp 6L.
Since the KZ has almost twice the HP as the Vulcan its a bit of a worry. But, I am betting the Vulcan is setup for parade type cooling, so the radiator might be ok for this use.