What is the Hole for??

I am restoring my 1972 GS Stage 1 car and am confused on the purpose of a threaded hole that is located behind the carburetor on the intake manifold. It is somewhat centered between the two rear carburetor mounting studs. Between the carburetor and the firewall. It is on the upper level of the intake (ie: Not the inlet for the brake booster). I tried to highlight the hole with a red circle in the attached pics. Any clue what this hole is for?
Thanks

 

The fitting for the vacuum to the modulator valve I believe.

 

Tom,

Thanks for the reply. Are you referring to the Transmission (TH400) modulator valve?

Does anyone have a picture or perhaps a P/N for the fitting that screws into the intake manifold?

Thanks

 

I did some additional digging and thought I would post my findings, in case others had the same question.

There is a single port connector that threads into the intake manifold (70-73 GM P/N 1369465). You attach ~1" of rubber hose to that single port connector and attach the other end to a hard line like this one "1970-72 Buick GS GSX Skylark Trans Modulator Line T-400" from inline tube. The other end of this hard line also gets ~1" of rubber hose attached and that connects to the transmission vacuum modulator.

Here is a diagram from the Buick Chassis manual.

 

This might help.

.

 

Redmanf1,
Thanks, that does help. You actually preempted my next question which was: how is the brake booster line routed? The second picture answers that question. I didn't realize that line was also a hard line.

Looks like we are in similar stages in our restorations.

Thanks again for the pictures.