Assuming you have your stock GSR manifold, NOS makes a plate system that fits in between the two pieces of the intake manifold. This would be your best bet. I knew a guy running a 125 shot on a stock GSR motor, but with proper tuning. The problem you're going to run into with the VAFC hack and 450's is during your daily driving. You won't have all that boost to compensate for anymore, so you'll run super rich. That being said, my friend had only a high flow inline fuel pump, colder spark plugs, aftermarket ignition, and a nitrous controller...and he ran 125 shot on a stock GSR motor. All it takes is proper tuning. Now I know people are going to come on here and say it can't be done, but it CAN, and it has. Now that's not to say that you won't run into problems. Whenever you're running that much nitrous/boost, it doesn't take a big problem to say bye bye to a motor. I like to use this phrase when it comes to these things....You play, you pay.