I pulled the chassis and opened the optical box. I thought that the spherical mirror could only be mounted in one way, bolting onto the rear wall of the box. While it doesn't have adjusters as such, now I see that the holes in the box are bigger than its mounting screws, providing some wiggle room:
Large washers go on both sides of the hole, so clearly some sliding back & forth was contemplated.
With all three screws loosened, you can slide the mirror a bit in any direction. Not foreseeing that alignment would be an issue, I have no record of exactly how it was mounted before I removed the mirrors. Nor do I know exactly where it was mounted when it produced the most recent picture, since I didn't know the screws had any leeway until I had loosened them all today.
I don't have a factory jig for aligning all this stuff, so unless someone has a better idea, I'll mark the box with tape tags showing the center of each mounting hole, and try to remount the mirror dead center in all three holes.
Also on my to-do list is checking the angle of the plane mirror to make sure it's exactly 45 degrees, and to ensure that each of the three side clamps is holding it the same distance from the struts (i.e., even if it's lying back exactly 45 degrees, it's not tilting sideways, either).
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html