2 Port vs. 3 Port DFP384 Electronic Feedback Carburetor

[Sephakrid]

While inspecting the various vacuum-controlled components around the engine bay, I discovered that my vacuum advance was connected to the manifold instead of one of the ports on the carburetor. Upon further investigation I found that the carburetor only had two vacuum ports! The 1984 and 1986 service manuals all show three ports. In addition, the spare electronic feedback carburetor I've been messing around with also has three ports. Does anyone have a vacuum diagram for a DFP384 carburetor with only two ports? Here are some pictures comparing the two types:

 

Two port:

 

Three port:

 

Unfortunately, the carburetor on the truck was rebuilt at some point, so I have no idea what version it may be. It does have the Hitachi logo on the side, so I doubt it's one of those cheap knockoffs floating around on Ebay.

Edited May 10 by Sephakrid
Clarity! Meant to say 1984 service manual

[datzenmike]

Front is vacuum advance, rear is EGR and canister purge. The missing middle one should go to the Vacuum Control Valve which modifies the vacuum advance signal under certain conditions.