Where should the vacuum advance be connected to on a 350 Chevy with 2 barrel carb?

On a 350 Chevy with a 2-barrel carburetor, the vacuum advance should be connected to a ported vacuum source on the intake manifold. Not the full manifold vacuum source.

A ported vacuum source only provides vacuum when the throttle is open (engine is under load). This is crucial for proper vacuum advance function; using manifold vacuum will result in incorrect timing at idle and low speeds. Look for a smaller port on the intake manifold; it's often located near the carburetor. Your distributor should have a vacuum advance canister with a hose barb fitting for connection.