Chevelle headers will probably work. Why ruin a nice GTO by putting the wrong engine in it?

The engine is 700 hp plus 13:1 compression and needs full length headers for performance. The car already had been changed once to an ls and debate is not the question. The customer wants what he wants. So I appreciate any help with information.

With that amount of heat I would get a good quality ceramic coated set. 13/1? Are you building this engine for E85? Any good hot rod supplier can fix you up with the correct headers.

I disagree with Ed on headers. With the right tail pipes and mufflers you can have almost any level of HP. I would use 3" pipe. Using cast iron manifolds would lose you a lot of power at the top end.

I appreciate all of your help. I however am running a race motor , and yes manifolds will drop the overall power by 75 hp. But my question is not if i can have custom headers made. I know manifolds and shorties will fit and I know a chevelle is very similar . I am curious if anyone knows for sure and has an actual part number that would work for full length headers.