mswilkes65Chevy,
If your engine has a points distributor equipped with a vacuum advance can then it needs to be connected to a ported tap on the carburetor. I'm guessing this is the case with a '65 six cylinder.
Some carburetors have more than one port but I believe some only have one and again, I'll guess that the little one you found is indeed the tap for the vacuum advance can. Lets see if someone shows up to confirm my guess. That port should be plugged now if there is no hose attached.
Stuart
