470 in a b body with 10.7-1 compression, hooker 1 7/8 headers into a 3 inch x pipe then into 3 inch 12 or 16 inch race bullets then into 3inch ultra flows dumped at the rear axle.

i now have 3 inch that was bent up 20 years ago and with an h pipe into an h pipe then reduced down at the muffler to 2.5 into super turbos. ive been thinking about something thats mandrel bent, flows better. i dont mid it being a little louder but i do drive the car a fair bit. i put 3000 miles on it last year so i like to be able to talk to people and listen to music

If you move the muffs to the rear of the car behind the rear end and let it dump out at the end the muffs with no tail pipes at the rear bumper it should be quieter than having them dump under the car
My old pump gas Duster was made that way, it was nice in the car at part throttle and got a lot louder at WOT
AKA aside, it did make it nicer in the car with the 14x7x3.0 Magnaflow muffs mounted back there between the sub frame and outer 1/4 panels

I would stay away from a true X pipe. At the cross intersection, the whole engine is essentially breathing through a single 3" pipe. The X pipes that have two 90s merged with a small hole between seem to be much better for all out power.

I agree with CB - end it far back.
Long bike racing history tells us that a "cap" at the end slightly smaller than the tube ID has a very significant effect on noise with little drop in power (except WOT), like 3" dropping to 2-1/2". It's also easy to modify and remove. For a test, a FLAP adapter ($5.00?) and a couple of pop rivets.

I have 3" Vibrant duals on my cruiser, and I wouldn't want it any louder, but it doesn't make much power on light throttle.