HELP - Rebuilding an original 67 400 to stock!!

I just bought an all original, highly optioned 67 Firebird (400 series yt motor), which has been sitting for nearly 20 years. I have been trying to buy it from the guy for over 10 years. It is almost all original (minus wheels) with the original paint. I think I can save almost every piece of sheet metal, but will have to replace a lot of the interior. I want to rebuild it back to original, but I want to add as much more power as I can. What can I do with the 670 heads and Block and anything else to make it meaner than when it left the dealership. I have a 67 Camaro also, but totally went the oppsite way with it. (550 HP now) Should I replace the entire bottom half with new stuff and keep the stock stuff?? I am confused on what to do. Can I rebuild the stock carb, where it really performs well or should I slap a new one on? Anything Ideas would help.......Thanks