A local muffler shop made the setup on my '69 using the original factory system as a pattern. One thing the local shop won't be able to do is to expand and ovalize the tailpipe tip as much as the factory tailpipes. They were stretched, flattened, and clamped so as to clear the leaf springs, and were cut at an angle to approximately follow the bottom line of the car. They drop just a little behind the wheel well. The system was also equipped with two resonators under the belly and one dual transverse crossflow muffler in front of the gas tank.
This is true for dual exhaust systems; I do not know how the single exhaust were done.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching