There was a special Vacuum line fitting on the front of the Pontiac intake manifold original .
Its now blocked off by the square head brass Pipe thread plug.
Next to the casted in Engine firing order 1-8-4-3-6-5-7-2 .
The vacuum line was constant engine manifold Fed.
The air cleaner thermostatic valve remsins closed in cool weather operating conditions.
Fall and winter.
It also prevents carburator icing.
Draws Hot air in through the exhaust manifold tin shield on Drivers side.
Ram Air 4 & 1971-72 455 HO Had dual hot air stoves.
All other engines single Hot Air Stove.
Does make a difference in Fall time driveability with near stock & mild aftermarket cams used.