Converting 318 to Dual Exhaust

I have a 69 Barracuda with a 318 and automatic. It was born with a single exhaust pipe. I want to install a dual exhaust system.

First question: Assuming my single muffler knocks down 60 db, when I install 2 mufflers, do each of them need to knock down 30 db (60 db total) to duplicate the amount of muffling in the single muffler configuration? I suspect it's not that simple...

Second question: I want the dual exhaust to have a better/louder tone/sound. Not over the top, but nice strong sound appropriate for a nice classic muscle car. Classic Industries lists mufflers with qualitative levels of sound inside and outside the vehicle. Any recommendations on which one to get?

Third question: Is there a dual exhaust setup you recommend to do what I am looking for?

THANKS IN ADVANCE!