Carter BBD tuning issues

Ok, so to add to this conundrum of mine, there is an unexplained, what looks to be a vacuum hose hookup that is fairly large on the opposite side of the carb from the idle adjust screw. I do not see it pictured or talked about in my manual, so I don't know what engine it's from. I looked at the numbers the other day but I don't remember them. I will post them later after work. Until then, does anyone know what this might be?