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Here is a postcard of factory #11 from around 1909.
This partial page from Don Bent's book (second edition) "A Place called Buick" Shows the exact same location as the photo below. The photo below I have seen on numerous web sites and they all have a little bit different explanation as to what is going on and the location.
Publicity shot inside of factory #11.They did not assemble the car here. There are some parts lying around, so maybe there is some repair work going on.