Calvin,
The quick answer is that the HS2 carbs that originally came on your Midget do NOT have ported vacuum. On HS2 carbs that DO have ported vacuum, it is on the front carb near the top of the throttle plate horizontally pointing forwards. These were present through the late 60's, but, since US emissions were mandated at idle (sorta made sense if you look at Chicago "traffic"), they needed a way to effectively tell the distributor that the engine was idling. Manifold vacuum does this much better than ported vacuum, but at a cost of not telling the distributor much of anything else. The bad news is that it is beyond most home mechanics to add ported vacuum to a carb, because it involves a precise hole or slot that is gradually exposed to manifold vacuum as the throttle butterfly opens. The good news is that you can rebuild a late-60's HS2 set (with solid butterflies even) and use your swung needles if you hate the centering process and get the ported vacuum. Just make sure that you keep the domes and pistons together as a matched set.
David Lieb