My old Duster had the 3.0 inch mufflers and pipes routed under the rear end housing due to having coil over shock rear suspension with ladder bars and a stock gas tank leaving no room for the exhaust to fit in there. We mounted the muffs between the rear sub frames and the outer 1/4 panels with the end of the muffs having a 45 degree short pipe on them exiting at and below the rear bumper
The muffs were a set of the older crimp style Maga flows ovals that were 14.0 inch long at around 7 to 10 inches wide with 3.0 inch side inlet with a center rear outlet
They weren't really noisy in the car at light part throttle driving but they got a lot louder at WOT above 3000 RPM
That car would pick up .002 ET and .2 MPH in the 1/8 mile by removing the complete exhaust system, it had Hooker Fenderwell headers and three inch pipes the rest of the way mounted like side pipes until they swung under the rear end housing to the muffs
That car had full aftermarket inner wheel wells all the way to the inner sub frames
Worked good, lasted a long time