As I recall, when they were introduced in the mid 70's they were sold as a set...the backplate pump and big bore "pumper" carb. They were first available for the K&B .61 and then the O.S. .60 FSR and ST G .60 and Webra Speed .61...then they were available as an option, already installed on the K&B .61 and .40 series 75.

Some (non Perry ) carbs work OK with the pump and some just don't have the adjustment range necessary to get 'em to work properly.