Yes, the vacuum fitting at the top of the carburetor is for those with emissions controlled engines such as if you were still running the stock lean burn distributor. In those engines, you have to run it at the high point because if you don't it will have too much advance at idle and burn up because the distributor is already set differently. when you're setting up a performance engine without lean burn and without emissions controls, you use the vacuum port at the bottom for full idle advance. That is also why your engine runs well at off-idle, but not full idle. That was the give-away, after reading your description of symptoms I immediately went down to the pictures hoping I would see a clear view of where you had that idle advance hose plugged in to.
