Muffler Specs?
 

So I recently decided to get a glasspack muffler for my blazer. And I'm wondering what would be the best specs for one. Example the best inlet/outlet size and overall length and if the new muffler should be centered/offset..

when i changed my muffler i went to a 21/2" to match the size of the tail pipe worked well all i had to do was add about 8" of pipe to lengthen the tail a little bit