I've seen similar vintage locksets (not Norwalk) installed upside down since the anti-friction latch was not reversible!
Pete Schifferli
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The Norwalk patent 420,174 of January 1890 was designed to offer master keying. When a particular application was to be operated by the change key or master key only, both offsets were not broached into the plug. IIRC, the offset left in your cylinder was used when no MK operation was required. The cylinders themselves had an external diameter of 1.250" which was unique to Norwalk products. The keys were not double bitted as you can see in the patent image below.
BBE.