Glasspacks are pretty simple critters. Each may have a bit different tone depending on the way they are built and the material used to pack them. The cheaper they are the less likely the material will last and the sound will change & get louder, my expereince it's more of an issue with engines that have higher exhause temps.
Personaly I'm still a fan of the good 'ol fashioned cherry bombs for the low cost option, but there are much better quality and longer lasting packs out there. Magnaflow makes some of the best IMO.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P