There will be no vacuum there when in neutral no matter how hard you rev it.
are you saying if we put it in drive, will we then see vacuum?
lewtot184 and R413 nail it, the flange (base) gasket cannot really interfere with either vacuum ports.
the front vacuum fitting, going to the distributor vacuum advance, is connected, more or less, to a port above the throttle plates inside the throat passage with the venturi. when the throttle is at idle, and the plates nearly fully closed, the port is "seeing" mostly non-vacuum air above the throttle plates. but as the plates are opened, the port is exposed to more of the vacuum from the manifold, and that is fed to the timed vacuum advance port on the front.
the side vacuum fitting, going to the choke pull-off, sees lots of vacuum at idle, and is fed along that channel shown in pnora's photo (upper left). note this channel is below the throttle plates, and is exposed to manifold vacuum as the engine is running and is sucking air/fuel, regardless the position of the throttle plates.
you should see vacuum on the front fitting, with the engine running (even in neutral, ha ha) as you open the throttle slightly. There may not be a ton of vacuum there, so a vacuum gauge can be helpful to test it.
As you rev the engine up, the mechanical advance in the distributor should be apply timing advance, too. If you're not seeing ANY advance, could it be possible your testing method and/or tools are to blame?
