Flowmaster muffler question

I'm looking to upgrade my exhaust. I like the sound of the flowmaster series.
I know the pro's and cons as I may lose HP but I do like the sound.
The question is do I have to go with their full cat back exhaust kit or can I just buy the muffler and get a shop to weld on a Y-pipe in order to get the dual exits in the rear I want?

If so what size of the 50 series would fit on my 08 DC?

 

YOu can do it however you want..... You can install just the muffler with your stock piping. You can install a muffler with new custom piping or you can buy the dual exit kit.

I have the dual exit kit....and I had it welded (stitch welded) after I had it exactly where I wanted it.

There are different types of flowmasters. I have the 50 series which is a nice tone and not loud. THe 40 series is louder. The 70 series muffler is the softest (quiet) but I don't believe it comes in a dual exit kit or even muffler.