The reason you can add 200HP safely with a S/C or turbo but not nitrous is this:
a supercharger and turbo build boost over a time period of a few seconds and do so in direct relation to the engine's RPM.
With nitrous, you go from 260HP to (in your case) 410HP in a millisecond. And can do so at any RPM you hit the button (without window switch).
This kind of shock on the engine internals and drive line is equal to about 600HP on a forced induction car. This is why people kill parts with N2O.
With the window switch, I would have the nitrous enguage no sooner than 4,000rpm, and cut off no later than 5,800rpm.
Total cost for a COMPLETE kit with the safety add ons is WAY more than a vortec kit and a 3.25" pully to run 10#'s of boost. Which with a very conservative tune get you at least 400RWHP.
And you could use it all the time, without filling a bottle.
...Just my .02