I had that same problem with a tripower manifold on a 390. Fought it for months and then decided to go back to a 4 barrel. Changed manifold and the smoke went away. I asked a big time Ford drag racer about it and he said look for a crack in the underside of the intake runner. Sure enough there it was, welded the crack, reinstalled, and smoke went away. I was told that many of the stock Ford aluminum intakes did that??? The crack was very hairline in nature really had to clean it well to see it.

John