It all depends on how clean is "clean"? The traditional method, and I agree with Bob, it leaves among the nicer finishes, is glass-beading. Sand is VERY aggressive, and I agree completely with what has been said about NOT using it. IF one turns the pressure down AND uses kiln-dried, maybe 60-mesh, it won't hurt so much. But sand has "sharp edges" unlike glass beads. If non-dried air is used with sand, it's like injecting rust into iron... I know, it's an aluminum intake. Not the point.
If you have a good automotive machine shop in town, call and ask if they have a thermal cleaner. If they do, it's usually accompanied by a blasting machine. Ours uses stainless steel "shot". You can "clean" the manifold first in a chemical cleaner (Aluma-Brite, transmission shops use it in their "jet washers"). DO NOT let anyone put it in a caustic solution. The media in our blaster leaves a "peened" surface that is both bright and "smooth" (it "folds" the surface irregularities) . We don't use the oven for aluminum, but many shops do (natural gas is okay, propane or electric is not). If your local shop maintains their blaster/vacuum properly, and use stainless shot, they can produce the same results. It's the closest thing we've found to "as cast" new manifolds from Edelbrock. It takes less time and is usually less expensive than getting it glass-beaded.
Like anything else, if left "in" TOO long, it can damage some surfaces. Trust your machinist.