Nothing to be confused about, see if this helps. What you are trying to do is connect the map sensor to see manifold absolute pressure, or what we normally call vacuum. To sense this the sensor bung must be located below the throttle blades. It also must/should/ highly suggested be located within the plenum so it reads all the pressure drops from all the cylinders. This gives a smooth signal and is why you don't want the sensor bung in a runner.
That diagram is for a throttle body that has multiple predrilled ports under the throttle blades to pick up the manifold pressure signal. It appears you have a manifold port in the lower center of each throttle body. When you remove the plug if that port goes all the way through the throttle body and opens under the throttle blades that's a port that you can tie in the MAP sensor to. You should be able to see this when looking under the throttle body as well of course.
The center section of your plenum, between the throttle bodies also appears to be a common area between the throttle bodies. In my mind that would be a better place to tap the hole for the hose barb and pull the map signal versus a single location at a throttle body. The reason is it's an area of the plenum that will see all cylinders. Again, a location that should give the smoothest map signal.
It's important to have a steady, smooth MAP signal if you are running a speed density EFI program logic. If the MAP signal is not steady and smooth it will be impossible to get a good idle or decent tune. The more cylinders the MAP signal is exposed to in the plenum the better. That is why I figured another option would be to Y the two throttle body ports together, then into the MAP with a single feed.
You will also need a manifold port to reference the pressure regulator if you choose to do so. That also needs to be a smooth signal otherwise pressure will fluctuate causing tuning hiccups.