Since we're all family here, it's your turn to do the dishes, Cait. I did 'em last time.
I posted a 1962 blueprint a few posts back. It's not very high rez, unfortunately, but here I've blown up a few places. This one is useful because, as Fenwright noted, there are some ridiculous assertions about the planning of the HM out there. I've had debates with more than one person who thinks the elevators may have been put in after the façade building was already built. Even Surrell's book absurdly suggests that Marc Davis's ride script from 1964 may have been the inspiration for the stretchrooms. This blueprint slams the door on these and other misconceptions, so you may want to file it somewhere where you can grab it when you need it.
Like I said, I wish it were higher rez, but the gist is there. The date is not easy to read, but it appears to be "3 - 19 - 62."
Now here's the kicker. Do you see the note in the upper right on the blueprint section posted above? "Garden Wall 8' Fencing," with arrow. There's our mystery structure once again.
That may be it under construction on the left in this photo:
Whatever its purpose was, it had a handsome brick archway in at least one place: