Ported vs. Manifold vacuum
With manifold vacuum you have vacuum from idle until almost wot and you don't have any vacuum at idle with ported vacuum. It will depend on your setup whether you need vacuum at idle. Do you have vacuum advance on your distributor? What is the duration of the camshaft? If it's a big duration cam with alot overlap where you have low engine vacuum and have power disc brakes you would probably use ported vacuum. Where is your initial timing set now? Set it around 16* and you should have a fitting that screws into the intake behind the left side of the carburetor. Another place would be on the throttle plate of the carburetor.