Hershball

I've been throwing around this idea in my head the last 6 months. I want to build a 383, w/ the lt4 hot cam set up in it. Will I need to have my computer reprogrammed after this, other than just to get more horse out of it or will the engine not run right. I have all the parts to do this, just have been waiting around to see what extra things I might have to do. Also I know you crazy go-fast nuts out there wouldn't care about this but how bad does the gas milage go down after you do something like this???