Can anyone help identify a carb I have. It has a cast iron top, attached with machine screws to an aluminum bottom. It was made for a Model "B" as the fuel inlet points forward, and has the throttle and air intake dimensions of a "B." Choke driver is set up same as all "A" and "B" carbs. Throttle plate has a "Z" stamped in it. There is a round ID plate with a single rivet on top with the number 2405N stamped in it. Any ideas??? Thanks for your help! - Mark