That is interesting because the base plates are correct for each carb. What are the dates on those two carbs? It should be a letter and number combination stamped in the metal tag (example: B7).
As for the vacuum line, if the hole has a plug in it then it was not used likely, otherwise the tube fell out.
Being it's an AIR carb, I believe there should be a vacuum line there that ran to the fuel mixture control valve / diverter valve.
I know that line is on my 67 LOS BB.
Here is some additional info: http://www.camaros.org/emissions.shtml#valves