bob look at the pics you posted. the inlet tube is stepped from 1 7/8 to almost 2.25 thats the lip john is talking about. on mine i had him cut the inlet tube right at the weld on the body and open it up to allow a 2.5 " tube be welded in its place.
john you need to measure your inlet as the setup for mine was cut off and the straight piece was welded in place to accomodate whoever bought it. i think its 2.5 but not sure and you may need to step back down to fit your n/a setup

also bob if you still have it look at your oem muffler and see it has amg markings on it. if it does i may buy it from you if you dont want it. gotta a desire to cut that open and see whats inside!