Forget everything you are thinking right now. lol. If you want a nice sound, you need a turbo. Like me, lol.
But I know you won't so I will try to help. If I were to build a supercharged motor again, these would be my only mods and to be honest, it would make equal to or more power and sound better than 80% of people who mod their GP's.
Headers w/ cutout
NIC cam
stock timing chain w/ 90# LSx springs
LS1 throttle body
Home-ported Gen3 (GenV's are still too expensive for me)
3" pulley
homemade FWI
Good tune
This should be your exhaust, All you need, Period.
Headers (comes with a 3" donwpipe) and an electric cutout placed in the lower downpipe. Leave the catback stock aside from some new tips if you want a different look. This is the best setup you can get IMO.
Best performance when cutout open (takes 2 seconds to open/close) and quiet when closed with a nice idle. If you want people to hear it if it's not loud enough, open the cutout.
You'll want a cam to reach 325hp, I would suggest a NIC cam. It's the best idle you're going to find for the 3800 and is the cheapest way to reach your goals.
LS1 and Northstar throttle bodies can be found fairly cheap and are a great upgrade to a s/c build. Port the inlet of the supercharger to match the TB.
Replace the timing chain and put on some 90# yellow LSx springs.
Those mods above with a 3" pulley will be more than enough to make your 325 hp goal and more than enough to eventually break hard parts in your transmission.