Bridge motorcycles,they had a few bits including a full race for £800 i think.It was all sold on ebay.As for the difference between the exhausts,i think it's to do with how quickly they get rid off the exhaust gasses i.e.the bigger the better.Plus,i fairly sur it would be louder.If looking on ebay,don't just type in ducati 749,use lots of combinations and don't discount stuff in europe from your search.