This photo, also in the CHM archive but not digitized, is probably of the same layout / computer: https://www.computerhistory.org/collections/catalog/10275791...
The PDP-1B was the production prototype of the PDP-1 and there were only 2, we know of. The first one (white) was intended for LLNL, but the order got delayed and it went to BBN instead, the second one (blue) became the actual LLNL machine.
Update: Curiously, the this page [1] also mentions a "PDP-lB" [sic!]:
[1] https://www.cics.umass.edu/about/history-school-computer-sci...
Anyway, this seems to confirm the Amherst link already suggested by Steve Russell.