He's coming around to it he just said he's going to modify his headers for a 2.5" outlet, don't bust his chops too hard lol.
Dusterguy, as far as I know long-tube headers almost always have at least a 3" diam. collector because that's the optimal size for the collector to 'taper down' to once the primary tubes have come together at the front of the collector. If you hook up a 2.5" exhaust you just use a section of pipe right after the collector that gradually goes down from 3" to 2.5". It's also kind of an "industry standard" so that different header models/sizes don't have different size collectors too, and in cases where you're making 500+ HP a dual 3" system will just bolt right up.
I'm guessing your primary tube diameter is 1-5/8"? You would also probably get a bit more power with 1-3/4" tubes, 1-5/8" is kind of the "entry level" size for smaller/milder V8s. Compared to making the rest of your exhaust bigger though it's really not important right now just something to think about.
Regards,
Khalid