Well, I'll just tell you what I did and see if something like this may work for you. I picked up a set of used Flowmasters for $30. They were under a truck with the turn down tips on them. While I was trying to figure out how to put them on my Suburban, I noticed when I rotated them to make it fit, the turn down tips would almost touch. I cut the turn downs off after I had the mufflers sitting where I wanted. Did a little test fitting and I could make the turn downs meet with little effort. So I welded them together and cut the tip off so I could get the stock tail pipe on it. Welded that up too. So I now have 2 mufflers going in to the same, stock tail pipe. I'll try to get some pics later if you want to see it.
I'm not sure exactly what you're wanting to do, but this is just how I worked with what I had to make the truck a little louder.