If you want that hourglass look, I've only seen it on internal headset-type headtubes. As far as I know, no one has attempted to do what you are doing and use a regular headset. I don't think it would work because the outside diameter of the upper and lower part of the headset may be too large for the cups to sit on squarely. It will be a considerable amount of time and money invested if you want to get your own head tube or cups custom fabricated by a machine shop. But if that's your cup of tea, then go for it.

He said he was going to turn his own 4130 stock. No big deal if one has the proper equipment.Here is the blue clue on how to do it. Start with oversize outside diameter stock like would be used for a 1 1/8" steerer, or even larger(assumes he is using a 1" steerer), and proper ID to clear the steerer.. Then machine the outside to shape as there is enough meat. Then ream the top and bottom to take 30.2mm 1 " standard cups.Finish up by facing the top and bottom surfaces so they are square.