That is almost exactly the same setup I'm gonna be running. I have the same headers 2 1/4 inch pipe with thrust turbo mufflers.
What is best true separate duals or and h pipe x pipe (the two sides connecting) ?
H & X seemed to be tied with the true duals right behind them. Engine Masters has a video on it on a low powered 350. IMO, run a X or H. An X sounds smoother, the H has a muscle car sound.
The only way to truly know is dyno test/track test. But ether is pricey
