318 Intake Manifold Question

I have a question maybe someone can answer. I Have a 1977 Dodge 318 engine, which is from a military Dodge M886 Ambulance I'm restoring. When I tried running the engine, it usually needed a little help from some starting fluid to start. It would only run poorly,(miss and sputter) at a mid range RPM or above. It acted like it had little or no engine vacuum. I rebuilt it's carb, but that did not help.
When I checked things out, I noticed, down inside the intake manifold, directly under the carburetor, a very clean,open tapped hole-- like something was removed. I have never seen anything like this in an intake before. The hole seems to connect the intake's planes, or something. When I checked out the truck's parts manual, it showed a part called "Plug, manifold vacuum control" which installs in the hole. So--
Does anyone have any insight or knowledge of this? Does the engine require this plug to run, or did it come from Dodge like this(open hole)? One guy told me, that the open hole connects the intake passages to the exhaust crossover, and the plug allows a tiny amout of exhaust to mix in to the intake stream-like a primitive EGR.
Bear in mind too, the truck was built for the US Gov't, and was exempted from emission controls in effect at the time-1976 and 1977.
So--anyone know what's going on here? Should the hole be open, or plugged?

Thanks!

Just plug it off... that was part of the EGR system.. you
dont need it.. that open port will be a big vac leak

Thanks MR_P_Body !

That makes sense-- I agree! Bear in mind this is a military surplus truck- maybe someone removed the plug-to make the truck not run well, the problem hidden- not repairable- so it could be turned in......
Hmmmm Thanks!

I know that when I was the motor pool sergeant we had a truck
that we would strip for parts.. it was gonna be turned in but
while it was still waiting for turn in we pulled parts from it

The EGR system connects the ports in the bottom of the plenum into the exhaust crossover.

IF the EGR valve is functioning properly and vacuum supply is disconnected, or EGR valve is blocked off, there should be no air coming out of those holes or standpipes.

Can it collect fuel? I guess so. From a neatness point of view I'd cover it or plug it. But they're pretty big holes. Anyone know the thread size for these plugs? Maybe NPS?

R.