Looked out for the care and welfare of an MGA back in the early sixties that had a Judson blower. Used a draw-through Falcon carburetor. The one with the glass float-bowl.
Too long a story to tell here, but we pulled it apart and replaced the Micarta vanes that made the boost. The inner drum was off center and the vanes slid out of 'spoke'-type internal slots to scoop the air. I imagine it made 4-5 pounds of boost when full on.
KS