I know when I had a Big Shot plate, the only thing close in NOS jetting was rated 350+ the jetting was .120N .116F.
I sent mine to have it flowed and Steve opened up the orifice in the nitrous solenoid. I can't remember off the top of my head, but I want to say for a 400 shot it was supposed to be like a .116N and .110F flowed around 5.5 to 5.75 p.s.i. of fuel pressure.
Like I said, don't quote me on that. Been quite a while since I ran a Big Shot. I'm sure someone will chime in with the right jetting if it's not right.