Nitrous is Very safe if you work with the right people. I would call Dave @ NitrousOutlet for a plate system.
I have run MANY different size shots on my hemi from a 75 shot to now running a 500 shot. Nitrous is safe, but do your homework and find yourself a great tuner to work with. If your are taking about running a 125 shot or smaller, its not that hard to get setup safely