509 purple shaft...???

So, maybe since this thing is fresh, I should get the four inch crank kit and do it now, since it would not need new millwork or bearings, 390 ci would see this cam like a 274 in a 318, by my math. would not seem so radical. since it is a good cam, why replace it? but then, I have kb's and a new forged crank, too, so why replace them? It would be more cost effective to just swap the cam, but I sorta want a streetable monster! Time, money, and realistic expectations... but I want to do it myself!! I don't want a crate, I know I can do this!