FWIW, getting the “airplane wing” shape is not that hard once you have plotted the interior curves for the individual cells. First, you build the individual cells with a consistent wall thickness. Next, you the build the vertical sections. The first step in building the vertical section is to lapp the cells so you get to zero thickness on both entry and exit sides. For each vertical section you would lapp two opposite sides of one cell for the center and one side of two others for top and bottom. The next step is to glue the individual vertical sections together and let them dry.
Now that you have the vertical sections assembled you lap them so they fit together in the horizontal plane. In the case of the 1803, lay each assembled section of three on the lapping surface and remove just enough material so all four corners zero out. After you have done that you can assemble the required number of vertical sections together to complete the multicell portion of the horn.
Simple really, all you need is more time than money and a bit of hand eye coordination.