I have a cyclocross bike that has top tube mounted cable braze ons. I cannot find a top swing derailleur that will go up to a 50T chainring so I got a bottom pull one. The part I am thinking of would be a clamp that will accept a pulley mounted below the derailleur so I can use the bottom pull. Some mountain/cross bikes have the proper braze on for the pulley. My bike has no braze on. Is there such a clamp?