When I was (much) younger - as in High School - I loved the sound of my Dad's '70 F100 4x4. 390, wide ratio 4-speed, 4.11's front and rear, (Thorley?) headers, 2-1/2" dual exhaust (no h-pipe) dumping under the back bumper and literally
empty 40" glass-packs.
When one tailpipe rusted out (ran the beaches of El Golfo de California a lot) over the axle; he had them re-done to dump out the side, just ahead of the back tires
and he replaced the "big hollow resonators" with new 40" glasspacks! 
I was
not impressed.
But by the time I was ready to move out of the house, I had least half the glass blown out; and it was starting to sound "good" again.
When I bought and later rebuilt my '72 F100 4x2 a few years later; my "engine guy" had a set of Ford cast-iron "shorty header" manifolds that came factory on a 68 T-bird 345 horse 390 - which fit like a glove on my new-to-me 406
.
He talked me into keeping the factory single exhaust (had to cut/bend/re-weld the left half of the y-pipe) and muffler, only going up to a 2-1/2" pipe for muffler back. Had a teeny bit more "throat" at idle and a bit more at WOT (if you were driving next to the exhaust dump); but it was usually drowned out by the sound of the motor trying to ingest/swallow the carb (at first an old AFB, later a Holley 750DP).
Took quite a few guys to school at stoplights; the class was "Stealth", lessons usually cost $20-$50 a pop, payable at the next stoplight. Also sounded quite righteous pulling a loaded trailer
Since then I've gotten a lot older; and since the '73 XR-7 looks kinda like a Lincoln Mk III of that era, I'm thinking of going back into the "stealth mode" - if nothing other than to educate some ricers with their fart-cans and airplane wings
