Suspect thermal vacuum switch

[Guest]

I recently did a lot of engine work on my 72 cutlass supreme, rocket 350 Rochester 2GC, w a/c , ie. all new ignition components, fuel pump, vacuum hoses and carb rebuild. Car runs great except for slight balk on initial acceleration, I am suspecting the vacuum advance is not getting suction from the 4 port vacuum switch attached in the top of the block as i am not feeling any suction in the line when i rev the engine. Autoparts stores listing a 3 port switch for this car.

Currently, 1 line from front of rochester 2 bbl goes into the top of the port (on a vertical connector and has strong suction), 3 lines on the horizontal connectors including 1-to vacuum advance, 1-to a tee fitting joining line straight off manifold and on to tranny and 1-to rear of carb, anyone know how to turn this 4 port configuration to 3??? Or have info on obtaining the 4 port switch? Or better yet have a vacuum diagram?? My chilton(s) are lacking in this department, thanks