The ls3 intake only fits a rectangle port head. With your Lq4 , you will probably want a Dorman ls2 intake. It does require a bit of work with a truck accessory drive to make the throttle body fit. Brackets are available to do this from Ict billet for instance. 477 is a real stretch and a very dedicated drag race build. So what are you looking for in idle quality and the rpm you want to turn? How will the car be used? Are you looking to bolt it together, or are you willing to get pretty deep into machining things. The budget and your ability to do your own work plays into it.

$1000 gets you cam and valve train and the next 5% hp will cost you another $1000 and quite a bit more effort.

Using the Pro Ls stage 3 412 whp unlocked converter number just as a basis; the next place to spend money is heads. The Tfs220 Heads get you the compression and flow and already have the spring pack you need with the Stage 3 cam so you can save that money. You will hit your 450 and closer to 475 number easily without machining. It will have good bottom end and will make your tuners job easy. Also fun to drive with 400 ft/lbs + starting at 3500 rpm

is there a way I can get close to that without aftermarket heads?

Not really. The big 317 chambers could be milled .030 and still fit pretty easily. That will help, but compression only jumps a little. The heads are still stock and don’t flow welll. If you mill .030 and swap the spring pack, you are realistically looking at 420. That being said, if you’ve never experienced 420whp, that will make your Chevelle really scoot and you can always add heads later and sell your old 317’s with spring packs to a turbo guy.

Agreed this is a good mid-range deal along with work by Total Engine Airflow. Our main point is the 5cc smaller chamber even before milling will help you get to your goal quicker.