My old pump gas duster had a set of the Hooker 2.0 inch A body fenderwell headers with a full 3.0 inch pipes exhaust system with a set of the early crimp style Magna Flow 14 long x7 inch oval with 3.0 inch side inlet with a straight through perforated pipe exiting in the center mounted at the rear bumper. the header pipes from the collector ran under the rocker panels like side pipes(which hid the ladder bars very well and then under the 8 3/4 due to the coil overs being in the way to run the pipes over the 8 3/4 rear end housing. that system was fairly quiet at light throttle cruise but it did get a lot louder at WOT. I later switch those headers to a set of Hedman BB A body 2.0 inch primary pipe size to get more tire clearances which helped a bunch
That car ran 10.69 on it first pass at Woodburn in October of 2005 on pump gas with the air cleaner and complete exhaust system hooked up, the motor was a 400 block stroke to 4.25 with a 4.375 bore and a true 9.15 to 1 compression ratio and low deck six pack set up on a set of ported big valve 906 iron heads
The Hooker collectors are under the floor of the car, the Hedmans collectors ended up in the fenderwell with a slight bend to go a little under the floor, not much under the floors though
On your car you could use a set of the oval muffs mounted in front of the rear tires under the rocker panels to reduce the noise with a 3.0 inch pipe or 3/5 inch pipe from the collector to the muffs