We came to a compromise. I really wanted a full dual system from the header back with a X pipe. The decision was made to keep the more common single outlet header. We are keeping the stock head pipe size of 2.25. Going into a Flowmaster 2.5in Cat Convert and then keep 2.5in into the muffler. We will then try a Flowmaster 40 Series 2.5in Single IN/2.25 Dual OUT Muffler . I will probably go dual 2 inch out the back.
He says I am going to hate the sound. I have heard dual exhaust in line 6 cyl, and think when done right they sound good. If it sounds as bad as he says it will, removing the muffler in favor of a single In/single Out will be easy. And only a small financial hit as compared to a full exhaust replacement including header.
If I do go single, I have thought about dumping the exhaust pipe straight down after the axle before running it out the back.