With the help of a number of members of OHS, and an appeal on the Facebook page of Organs of Mexico, I had a response from Jesús Bernal of the University of Mexico: “You are seeing [above] a superimposed fake facade over the real organ behind. It was a 1902 Schlag organ bought for the National Conservatory because the Amphiteater was used for many concerts as a second Conservatory auditorium. This organ was unfortunately destroyed in the 1980s.” As the organ builder went out of business in 1923 we are not likely to find what the covered organ was, unless someone has a specification. It was a long search that led to the making of many contacts and finding out a lot more about Mexican organs.
Sadly unless one can find a concert program perhaps, we are likely to never know the specification of this instrument. The sheet of six stamps is SCN 2695, the individual stamps are a, b, c and on the second row, d, e, f. All of the stamps are denominated $7.
I found this image for the music department at the university. One wonders if the arched opening in the wall is the very one shown in the stamp, with the non-speaking facade filling most of it?
The Mexican post office also issued a 100-label charity pane showing many of the same elements from the postal-use pane. The funds raised were designated to tuberculosis relief.
The sheet is quite large, not quite fitting on my scanning device.