Hi all. I am going to need your ever trusted experience on this one.

1. Did all 1968 firebirds have a dual vacuum control on the distributor? As standard?
2. Or did only Californian Cars have the dual vacuum control?
3. Or did only the 400's have the dual vacuum control?
I am trying to verify if my vehicle originally had a dual vacuum control. 1968 400/automatic/ps/ac/
Original distributor is #1111270
Original vacuum control is #1973412 (I think)but I am unsure if this is a single port or twin port vacuum control?

I have the 5 PORT thermostatic Vacuum Switch (TVS)on the manifold.
My research suggests that all 1968 birds had the dual vacuum control on the distributor (for emissions) but many firebird owners have elected to replace the original dual port vacuum control with a single port.(to prevent overheating during idling)

Next question is if I decide to go with the single port vacuum control on the distributor- which part number would be appropriate considering the car originally had the dual port vacuum control?
I understand that if I do go with the single port- then the relevant ports on the TVS will have to be bypassed according to details as outlined in other threads (vacuum advance)
Any help will once again be greatly appreciated from you all.

thanks
claude -Melbourne Australia

I suspect all '68s got the dual vacuum advance/vacuum retard. A '68 Pontiac Technical Service Bulletin disconnected the retard function port and plugged off a carb port and two TVS ports (a loop made) in many applications.

Thanks Jim
Your are correct all 68's had a dual vacuum.

thanks again.