In the past I had often used a over sized refective heat shield. Made from thin aluminum pie plate material and installed between the carb and insulator block.Form as needed to block out carb from heat radiated from the engine. They can do an excellent job at keeping radiated heat away from the carb body.
BTW, The carb mounting screws should also have heat insulation measures at ALL contact points. Don't underestimate the heat transfer that takes place
