According to what I've read, and been told, the hole in the roof was there because there were no dies or press machines big enough to stamp the entire roof in one shot, so they were made by stamping and welding the four corner sections in, and then installing the oak bows to attach the headliner to. This went away when the roof could be stamped out in one piece. As a machinist, I understand completely how much force and power it takes to stamp such a large sheet of steel, and such a deep draw as well. It does, however, never cease to amaze me, how many people ask me if the roof opens on my 35 Tudor!!