Denny, terrific job of sleuthing. I remain mystified, if a building was constructed on that site why it would be torn down? Costly to build and costly to remove unless it was damaged beyond use by fire.
I searched the aerial photo series amongst the OpenSFHIstory collection. From 6/27/1969, section 62 of 284 images shows the lot at the SW intersection of 25th & Noriega remains undeveloped at that time. You S.I. alums from that period will be curious to see the ’new campus’ that also appears in this image. https://opensfhistory.org/opensf/search/index.php?q=aerial+photo+1969&_ds=1&bn=1&bs=50&so0=contains&so1=contains
For anyone curious to browse that series of aerial photographs of San Francisco use the OpenSFHistory search window and type: ‘aerial photo 1969'