Nick, your on hopes and dreams if you think your Zex kit can even flow a 400 shot, yet alone a 250.
for a 400 shot you would need to have one separate fuel pump just to support the fuel for the nitrous. What fuel system are you running? dual 255’s or what?
you have never used nitrous before have you? to make claims about running a 400 shot without even starting small is ridiculous. You will need to run so cold of plugs that are obviously non projected that you wouldnt even be able to drive your car N/A from stop light to stop light without fouling.