In general there are two types of engine vacuum - ported and manifold. 

Ported vacuum is used for things like timing advance / retard, or other 
emissions adjustments. Ported vacuum is taken from just at the edge of the 
throttle plates travel, in the throttle body throat. Closed throttle plate, no 
vacuum to the port. Open throttle plate, that is, press down on the gas pedal 
some, and the edge of the throttle plate will expose the port to engine vacuum.

Manifold vacuum is used for just about everything else -�heater actuators, 
headlight doors (OLD SCHOOL!), cruise control actuators, etc. And in this case 
gages.
So, any vacuum tap that is not near the throttle plate will serve for you. The 
one on the air distributor body is the best choice.
�Evan Mac Donald 

"...in the absence of facts, myth rushes in, the kudzu of history."
-Stacy Schiff 

________________________________
From: John Lauterbach <jhlauterbach@BELLSOUTH.NET>
To: vanagon@GERRY.VANAGON.COM
Sent: Sat, December 10, 2011 2:13:11 AM
Subject: Checking engine vaccum

If one puts a Tee in line between intake manifold and fuel pressure
regulator and then connects vacuum gauge to the Tee, will that give a
good measure of engine vacuum at idle speed and say 2000 rpm?

John