Here is another idea that will be acceptable to you. You can manufacture a manifold as per the sketch in mild steel material and use straight rubber pipes connecting the carbs to the manufactured mild steel manifolds. I would suggest using 10mm thick plate (will not burn while welding) for the flange and a short piece of pipe of suitable diameter and length, weld the two. Paint. Get a straight hose pipe of suitable diameter, cut to suitable length, use good quality jubilee clamps to tighten everything up.
Oh yes, you will need a thin rubber gasket between the newly fabricated mild steel manifold and the inlet manifold or cylinder head.
