The old 19th & Lincoln photo shows the columns lining up pretty much with the end of the wide sidewalks. In this 1964 photo, the same gas stations are there, but with very narrow sidewalks and the columns still look to be in line with the edge of the sidewalks. I'd say they were moved back at the time of the road widening. http://webbie1.sfpl.org/multimedia/sfphotos/AAB-5962.jpg
I'd be willing to bet that whatever monument was just inside the Park in the old pic, that it was moved to some obscure corner of the Music Concourse. Old Uncle John McLaren hated encroachments into "his" Park, and usually planted fast-growing trees and shrubs around the statuary.