my engine

I have a 66 GTO with a 400cid engine from a 73 Grandville and am getting ready to have the engine rebuilt. I know very little about engines. I would like to open up the hood scoops on the car to make functional ram air but am not sure what to tell the engine shop to do the engine. I'm not really sure what changes should be made to the engine to set it up for ram air, but i'd like to be able to go into the shop and tell them exactly what needs to be done. I'd like to get about 475 horse power from the engine, how hard is that to achieve from a 400 engine?
I know many of you probably have the knowledge to help me, and i would really appreciate all replies.

Thats a pretty big chunk of horsepower out of a 73 400. I guess you need to get a little more info on the Ram Air package. It wasn't just opening up the hood scoops, they were actually plumbed into the air cleaner. Why the 475 HP figure? What do you plan to do with the car? How much do you want to spend on the Engine? Do you have a beefed up TH400 to put behind this thing? Rear End? etc... Give a little more info on what you plan to do with the car 90% of the time, and I might be able to give you some useful tips on how to get there. Oh, and don't get too pumped up about having a car that makes gobs of horsepower at 6000 RPM, unless you live at the track, and have a big wallet. You were right to come to this forum and ask though, there are a lot of sharp people in here. Good Luck.

Macktoschool, good job! Many would just tell him to build a Chevy... The 400 is a great engine with a ton of potential. The heads from the '73 gotta go. '70 and older or '75 and newer, unless you can afford the round port stuff.
There's a new book out by Jim Hand, pronted by SA Designs, called "How to Build Max-performance Pontiac V8s". You will find all you need to know about building a street Pontiac. The horsepowr number you're looking for is a tall order for a pump-gas 400, but 475 lb. ft. of torque isn't. There's an old saying that fits here: Horsepower sells engines, torque moves cars" This torque output is what made GTO's reputation. And it isn't from losing...
You can also go to classicalpontiac.com or boyleworks.com (muscle cars) for advice from the "gurus" in the Pontiac family.

Thanks.

Lot's of power going on there.