New guy to big block world, need a 400HP 383 Recipe

The factory rating is a little misleading anyway. They would tune for each rpm point and then take the highest numbers reached for each point, and publish them. Dyno technology is much better, machining technology is much better (if you use a shop with modern equipment), piston and ring engineering has come a long way, head theory and machining technology is light years ahead... So a "stock" engine using "stock" parts can be made much more powerful now. It doesn't take much more than a cam and exhaust to get really good numbers.