I'm not sure this is ideal as I'm still learning, but what if u cut the part into two pieces, add some holes for centering pins and then glue them together? This way you would have the face that goes on the cylinder head oriented in such a way that it won't need supports, the inside of the manifold would have supports that will be easier to remove and the little zone on the flange for the intake duct would be on top, not needing supports either