The muffler that came as part of the RalliSpec catback is a Magnaflow, but I don’t know the PN.
The sound is V8 awesome and rumbly (I’ve got a Borla header too, mind you). On decel, it sounds off a mild burble. Even Trey of Cobb Tuning (who’s probably heard it all) thinks it’s ‘awesome’. I strongly suggest a midpipe resonator to go with it – kills the ostensible mind-numbing drone.