just got me a '67 Barracuda

IF blocking the air horn makes it run better you definately have a vacuum leak.
A bad PCV valve can cause all the symptoms you described also since it works on vacuum. If you have vacuum operated choke breakers , or spark advance, or power brakes, start pinching rubber hoses with pliers to rule them out or discover the culprit. Good luck
Also... IF the fuel air mixture is wrong ( vacuum leak ) there will be a timming place where it will run
but poorly.