I know the ones for the biposto S1K were aluminum with "race only" stamped around the end ring vs stainless with "e1" and a bunch of numbers for the homolgated ones. Both have removable db killers, but the stainless ones also have packing inside and I believe cats. I know holding homolgated can up and looking down the end you can't see all the way through whereas I believe in the race version you can.I had thought that the GT Termi kit had optional removable db killers making them street legal. Though I could easily be wrong, which happens a lot. =) I'm a late comer to the Sport Classic line so I can't say for certain what was available at the time the bikes were being supported (accessory wise) by Ducati.
That being said, no idea what they made for the GT