So the 6.0 is like the older Vortec 350's with dual cats into a dual in single out muffler, while the 5.3 and 4.8 is like the older Vortec 305's that have a y-pipe into a single cat into a muffler. Awesome i have always wondered about the 6.0 and 5.3/4.8 headpiping differences.

peace
Hog

 

The 4.8/5.3's still have dual cats in the y-pipe, but the 2 down pipes from the manifolds join into one after the cats, which bolts to a single in/out muffler.