Man I just spent 15 minutes on a reply and the system lost it !!!!
Here I go again.
There are a bunch of things that affect sound. On a V-8, firing order changes the way an engine sounds. You can actually hear the difference between a Ford 5.0 and a 350 Chevy.
Camshaft design can affect sound. A longer exhaust duration and a tighter lobe separation make for a louder engine.
Compression ratio affects the sound. Higher compression, equals louder.
Engine size affects sound. If you have two cars with the same everything except size, the larger one will be louder (think Pontiac, Buick, Olds) The smaller engine will also sound crisper. Think big block vs. small block.
Exhaust pipe size changes the sound. Larger pipes make more noise. A 3" system is WAAAYY louder that a 2" system.
Muffler design makes a difference. In talking about mufflers, a larger muffler makes more power and is quieter than a smaller muffler.
A two chambered Flowmaster is louder than a three chamber (50 Series), but the 50 makes more power. A 70 series big bodied three chamber makes more power that the 50 series, but is quieter.
I particularly like Dynomax mufflers. They are a combination of a chambered muffler that also has packing. Their welded mufflers include Race Magnums that I think are pretty loud. Their bread and butter muffler is the Super Turbo. The Super Turbo have a 17" long body and are fairly loud, but they don't have the interior drumming that a Flowmaster has. I run Hemi Super Turbos, which are a big Body Super Turbo. These are 23" long and are quiter and make more power that a Super Turbo. They also make the Ultra Flow mufflers. An Ultra Flow is a Super Turbo with a stainless case.
Many manufacturers make packed chambered mufflers, and Edelbrock even sells a kit to repack their mufflers (what a concept).
Turbo mufflers are usually inexpensive generic stock chambered mufflers that have some sound(but not much tone) because they are short, and have some power because there is not a whole lot of chamber size.
Glasspacks (and steelpack such as Smitty's) come in lengths from 6" to over 48". The longer it gets, the more mellow it gets. Anything over 30" or so has that classic "motor boat" sound. Because it is a straight through muffler, it makes decent power but in shorter lengths it will be loud.
System configuration makes a difference.If the system has an H pipe or an X pipe, it will be mellower and make more power. The H pipe increases low end power and smooths out the exhaust pulses to take the raspyness out. An X pipe seems to do it better, because it actually forces the flow from each side to mingle.
In some cases, headers will be a little louder than cast iron manifolds primarily because the cast iron soaks up some of the sound..But there is not a significant difference. The quality of the sound is different because headers make a unique underhodd noise that, to me, is not unpleasant.
Vehicles that have full tailpipes sound crisper and less resonant (droney) than those that have turn downs under the car.
I lost a bother in law to carbon monoxide poisoning, so I am very careful with preventing CO to enter the passenger compartment. If there is a compelling reason to not run tailpipes out of the back, I will at least kick them outside of the body line ahead of the rear wheels. I prefer to have them come out the back, but kicking them over the axle and then out the side behind the rear tire is a good option.
Tips affect sound, but not significantly. A flat tip will make the sound raspier, a turn down will lower the sound, a round or oval tip bigger than the tail pipe will magnify the sound a bit (That is why they call them Echo Cans).
If you want to really throw a monkey wrench into all this, compare the sound of a V8 with that of a straight 8 with duals (one of the sweetest sounds ever), or compare a v8 with a straight 6 with duals. Then toss in a v6 with duals and it gets even crazier....The differences are all related to crankshaft phasing, firing order, etc etc.
Then we get into sound quality. What is loud to me might not be loud to you. What I think has a good tone will sound ratty to someone else.
At my shop, we sold 40 series Flows if the customer wanted it loud, and Super Turbos if he wanted it quiet..But sometimes it didn't work out that way. I vividly remember a Ranchero with a 351C that we put Super Turbos on, and it was so loud, the guy got stopped on the way home from my shop for noise. We finally got it quieted down by adding an H pipe and a pair of 9" glasspacks in each tailpipe...I had trouble getting my 383 powered S-10 to quiet down. I put Flows on it and couldn't stand them. I put super turbos on it and it sounded like it had some really short glass packs on it. I finally put DynoMax Z plus mufflers (like a Hemi) and finally got it quiet...We can't have a 12 second sleeper that is noisy can we????
The answer to you question about a stock 350 with glasspacks is that, if they are long enough, it will sound great...I would go with 32" and an H pipe...It will sound really good.