I've finally changed my distributor to a dual advance one  but the Holley 4000 has no vacuum port to supply either direct or ported vacuum. I would prefer to use ported vacuum, but can see no way to get it. Rather than "T" off the line to the wipers for full manifold vacuum, I'd like to add a fitting to the spacer plate to provide a separate supply, but don't know whether to tap into all four holes or just the front two. Any ideas?? Thanks : Bruce