how hot is too hot

yeah put one of those thick heat barrier gaskets under the carb. the holley carbs are a little better for that reason as they don't have the fuel bowl sitting right on the hot manifold. I had the same issues with my edelbrock and the gasket fixed it. even though you have the adapter its aluminum so it transfers all the heat to the carb. also if the air cleaner setup is low down to the manifold that will draw in heat and keep it around the carb. like an air dam.