The following diagrams from the '68 Diagnostic Manual should help you. They show all the routing, functional diagrams, etc. for that vacuum system. Although the diagrams for '68 show the use of all five of the TVS ports but a Pontiac Service Bulletin (T-2 if I recall) later eliminates the vacuum retard function and loops/closes off two of the ports. If you would like to see the '68 Service Bulletin, I believe I have one somewhere. Just let me know and I'll look for it and send it to you.
