You can't modify those systems, make 50HP, and NOT have to re-program the PROM. It's just the nature of the beast...they use manifold vacuum to determine engine load, ANY change that increases engine flow (which is anything...heads, intake, headers, cam, you name it) changes engine vacuum and negatively influences PROM programming. Not to mention that on top of driveability problems, you will also start running lean under heavy throttle, which can destroy the motor.
Hate to say it, but you need to save your money and spend it on the parts that will be needed to put the 383 in the car. Do things right the first time, you already have the motor, or you will be kicking yourself afterwards, knowing what you SHOULD have done, but having wasted money on something else.
If I'm not mistaken, nitrous needs additional fuel, since the ECM controls fuel here, wouldn't that incur additional changes/cost?
Edit: Thumbs down for everyone but no post to help the question asker? If you disagree, might be helpful to the question asker for you to say why.