Mufler, catylic convertor, headers etc

hello again

Ok so I am looking to replace my mufler, catylic convertor and I don't know what else lol. Here is the thing, my current setup has flowmaster setup all the way. Its a chevy caprcie 1991 sedan as you know so it is only one pipe, Can I make it dual? Would it be worth it to go dual? Or can i just leave it single and replace mufler/catylic convertor with some good ones? Any suggestions? What brand mufler and catylic convertor should I use for some good deep sound and to pass air care at the same time.

Thanks