Bear in mind that the maximum aperture is usually smaller than the front flange size, and you need to account for both dimensions. Also, it is often possible for a good machinist to make the opening on the shutter just a bit larger and the flange on the lens a bit smaller, so that parts that won't exactly fit directly can be made to fit. That is probably what would have to happen to get your 24" Artar into a Copal 3 or Ilex 4. With an Ilex 5, you would require two adapter rings to mount the front and rear cells of the Artar to the shutter, with no machining required on the shutter or the lens cell housings.