Emissions on my Slant

That last picture (With the two fingers in it) is a vacuum port, most likely for the brake booster, if it has power brakes, & it probably does if it's a 1976. It will run very poorly if at all, if it's left open because it would be huge vacuum leak. Get a good service manual first off, they are a gold mine of info. Haynes manuals aren't very good, trust me.