Classic/Antique Car Repair: 400 pontiac, pontiac motor, valve size

Question
I have a 1973 pontiac motor according to the numbers on the motor it has 175/185 horse power. i have seen other 400 motors with 360 or more horse power in earlier years. what do i need to do to increase the horse power of the motor i have?  can i bore out the engine 60 over, or will that make my cylender walls to thin? also if i bore the engine 60 over will the stock heads i have be okay. or should i increase the valve size. will the stock crank be okay? I'm trying to increase my horse power to at least 400. PS I allready know about cam, carb, intake & egnition,

Answer
You say you already know of cam, carb and I presume you meant ingition, but you never once considered dropping compression and going with a blower. I think you could geet there faster and cheaper, Don't think there is enough in your motor to go the other way.