For now... plug the vacuum line. Worry about it later.
At this point focus only on checking the engine and getting it ready to be started. Since it sounds like the engine has not run in 20+ years, start with mechanical things.
Mark and remove the spark plugs.
Make sure the engine is not seized from years of sitting. Find a very large wrench and put it on the front pulley nut. With the gearbox in neutral, turn the engine clockwise (looking at the pulley).
If the engine turns over with the big wrench, change the oil and antifreeze. If it does not turn over with the wrench post back here and let us know.
With fresh oil and a charged battery, remove the spark plugs so there is no compression and turn the engine over on the starter until you see the engine has developed oil pressure.
Once you have gotten to that point post back. You will need to go through the ignition system, set the static timing, and do some basic carb checks and adjustments.
With a car that has been off the road for 20+ years, plan on rebuilding the brakes and replacing several brake components.