Hooker super comps too big?

I'm putting in a set of super comps in my bird but I think I got a set with too big of primaries. They were a set with 2 1/2 in. primaries, full length round ports and a 3 1/2 in. collector. I'm planning on getting a 2 1/2 in. pipe system. Will they fit? It's too late to return them. I got them Jet-hot coated already. Will I lose a lot of low end torque with the headers compared to the stock manifold? Or will the gain be higher but not as high if I had gone with the 1 3/4 or 1 5/8 primaries? What should I expect, or do?

With headers you can lose or gain hp just depends on your set up. If you run headers with a smaller exhaust pipe it will be loud but not as loud as larger exhaust also with smaller exhaust you will gain some horse power but can be harder on your motor. If you go with a bigger exhaust say 3" for example it will be louder than hell but you could lose hp. In this case i would talk to a shop thats an expert on exhaust depending on what you wanna do weather just street or race. They will be able to help you decide what you need.

What would cause there to be harder strain on the engine, just by adding the headers, new exhaust system and muffs? I thought it would help it breath better. I want it for street/ strip use. I don't really care as much about the sound as I do about the performance.

The first question is: What year and engine do you have? For a real Pontiac, there are only 1 3/4 SCs for "D-port" heads and 2" for "round ports". I've never seen a 2 1/2 primary tube for any application. Even our nitrous MONSTER small blocks run no bigger than 2 1/4" primaries.

I might be wrong, I think they're the 2x27 with round ports.the collector size is 3 1/2 I have a 73 formula with a 400. The engine code is 889450 XN. I don't know what that means exactly but maybe it helps. I have the 4 X heads.