You neglected Goerlich's XLERATOR. They make one that is 18" and will fit right on A-bodies (we run them) and they outflow the Magnaflow and are significantly quieter than any Flowmaster. They are one of the only 18" body sized muffler, like the stock Cuda ones are so they are easy to fit on. Like MagnaFlow, their 18" one can be bought in offset center, 3" in and out. The Goerlich number is X119. They flow about 97-98% of an open pipe so they are great for power and they are about 8 to 10 dBA quieter than louder, chambered mufflers at 3500 rpm on a big engine (474 cu in.) engine.
Tom