Left side? Do you mean passenger side or Driver side? The plastic piece on the passenger side should be the choke. I checked my Edelbrock manual and also checked the 1406 on my car and there are no vacuum fittings on either side. Only two on the front and one at the back. The front one that is closer to the passenger side is ported vacuum and probably goes to your distributer for vacuum advance. I have the rear one going to vacuum accesories like cruise and the heater, the front one is capped and not used. I bet the one you see is actuall going to the ported vacuum and is just routed under the choke housing. Check to see if it came off the distributer.

Hope this helps
Pat