If you wish you might use my method that I “invented” or my Fundamental Chanel. My MF Chanel horn uses a sophisticated harness with centering functionality but in but Fundamental Chanel uses a very simple “extended ring” method. It us chip, it would cost very little any machinist to do it. I think I paid $100 for a pair of rings. Lake the rings a half or 2/3 of the size of your S2 driver thread. All the rest is visible on the drawing belle. The only pain is to co-axis the horn and the driver… But wish you it to be the only pain you have.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche