Flowmasters too LOUDDDD..& Cuda Duals...

I don't believe you can tell by a stamping number (they have a label that burns off) what series they are. You will need to get the exterior dimensions and compare to the specs on their web page. The Delta Flow versions were made specifically to kill the interior resonance. You may be able to tell by seeing a distoration in the metal on the output end of 2 or 3 Cheverons ( <<< )pointed toward the input end.