I had to get hearing aids last year....The noise from my truck affected them (causes feedback)....I ended up putting a pair of stock NAPA mufflers on it. I work at NAPA so I could go into the muffler room and measure what I wanted. Ended up with a 23" muffler with 2 1/4 inlet and outlet....Nice and quiet. The parts guy said they can look up sizes, so they can match what you need
Also, if you put a balance pipe in your system it tends to quiet things down.