Don't really have a direct answer to either of your questions, but I did put Thrush turbos on the Cutlass when I first put it together. Didn't really like them that much, they were kind of quiet for my taste. But then, I'm one of those Flowmaster guys. Put Super 44s on it last year, and am pretty happy with them.
I currently swapped back on the maybe 2" dual exhaust with manifolds, angled glass pack's into the crappy 2.5" custom tail pipes on my 70S. Sounds good, no drone. The Sanderson's shorties into the custom 2.5" head pipes into a compact X pipe into a Hooker cat back system off my G body. First no tail pipes, then full, droning and no where as good as it sounded on my 88 Cutlass, here is the clip on my 88. I am putting the system back on.
I am planning on Thornton shorty headers, Ram air down pipes into glass pack's then into straight through offset mufflers into Flowmaster tail pipes, all in 2.5".
Don't know if I've ever heard glasspacks on an Oldsmobile, they sound pretty fantastic. They have a lot of the deepness I love with the Super 44s, might actually sound better than them. Hard to tell when they're not side by side.
It's also funny the way different cars react to various exhaust systems. The system on the Cutlass dumps before the axle, and even though it's Flowmaster, there's no droning, but it's a little quiet. I have a '70 DeVille with Flowmaster 50s -- the quieter ones -- and a complete system, and it droned terribly. Both cars have about the same CR and factory heads, the DeVille has the factory cam, a crossover, and lots of insulation, the Cutlass has a bigger cam, no crossover, and much less insulation, and yet the DeVille is the one that had the drone. It finally went away after about 1,000 miles.
I will get a sound clip up of the glass pack's. They actually sound really good too, no drone and the right amount of sound, not too loud. As much as the exhaust droned at low speeds in the 70S, it sounded amazing compared any 4 or 6 cyl cars on the road.
Of course, V8s just naturally sound best. Had a kid flag me down in the DeVille, he told me it was the best sounding exhaust he'd ever heard ha ha. Something about the Cadillac firing order gives it a different sound... Oldsmobiles are different too, but it's not quite as striking. Look forward to hearing your glasspacks.
It does sound good. It is a bit quieter and no drone, the system off the G body, did on my 70. Now I just need to replicate that sound in a 2.5" system, I don't even think these pipes are even 2", maybe OD, pretty small.
G body system, Mandrel tail pipes exit behind the wheels, going back on this weekend.
The system on the 70 is just small duals, angled glass packs into custom 2.5" tail pipes straight out the back with Pypes stainless polished tips.
I have the system bolted back on to the headers. Then I noticed the 51049 filter, the long, big diameter Wix filter. I had to remove the inspection cover and barely got it out. It was only about an inch from the exhaust pipe. The Hastings LF222 filter will replace it, same size and similar construction as the Wix 51258. I have been trying to desludge this poor little 260, was gross under the valve covers. It runs decent but has a bit of a lifter tick, like a sticky one and low oil pressure, so I run 40 or 50 weight. I will probably go half 5W50, half 20W50 in this oil change with the small bottle of Risoline. It surprisely doesn't leak or burn much oil. I also found leakage on the front pump seal of the 2004R, not surprised but minor. Also the selector shaft seal is leaking. That is the second 2004R that has happened to for me.