Just a little update, I figured out what the extra off idle ports are for in the Olds baseplate. They are the discharge ports for the PCV. The Chevy baseplate has a totally different PCV discharge setup far under the throttle plates rather than just above like with the Olds basrplate. Inmother words, Olds uses ported vacuum for their PCV vs manifold vacuum for PCV like Chevy does. The PCV barb is at the same location for both baseplates, just the internal routing is different.
Believe me, I know how confusing it can get chasing ports on these carbs. But I think you're getting the Canister Vent Valve (CCV) and the PCV port mixed up on the Olds. Olds uses full-time vacuum for the PCV.
PCV comes through the 1/4" vent tube on the passenger side of the baseplate and vacuum is from the common area under the primary fuel well plugs that is open via rectangular "windows" cut into the baseplate for full-ride manifold vacuum underneath the throttle blades. This also provides the vacuum for the "Tee" port for the primary choke pulloff and air cleaner dampers. When the baseplate is bolted on, you cannot see the PCV porting route very easily.
The driver side has a slightly smaller tube on the baseplate that administers ported vacuum from either side to vent the Canister Control Valve. This porting is on the bottom of the baseplate. These are two small bleed holes above the throttle blades with a common channel "connecting" all 3. There's one more ported vacuum port on the front of the carburetor float bowl and that's for the EGR. It's not on the baseplate, however, but the end of that channel is and is respresented as a horizontal slot just above the throttle plate on the driver side.
Olds idle channels have an upper idle air bleed in the air horn as well as IABV air porting, a lower idle air bleed under the venturies along with a transition slot at the throttle blades. And of course, the mixture screw ports below the throttle blades.
These pics may shed a bit more light on this.