Carb identification

My carb looks very similar to this one and I was told BBD. Only difference is the odd looking thing near the top of the air horn at the firewall side. What is that? Also does it run ok with that vac line closed off on the pass side? mine runs from there back to the dizzy cap. I rebuilt mine this weekend with a GP Sorensen kit from our local Autozone. That kit had tons of gaskets and a new plunger. I even got the floats from the same company. So far all seems very well. The float part number is 779-1730B and the rebuild kit is 99-129C. hope this helps a little.